USB4 Optical NIC vs. PCIe Optical NIC vs. USB 10GbE: Is 10G Enough, or Should You Go 25G?
What’s the difference between these three options? Is 10G enough, or is it time to move to 25G? This guide will help you decide.
For anyone new to networking, one question comes up again and again: you want to speed up your NAS or PC, but once you search for a “network card,” you’ll find three completely different types of products.
Some go inside your PC case. Some sit on your desk. Others look like oversized USB drives. Prices can range from a few hundred RMB to several thousand.
So what’s actually different between them, and who should buy which one?
This article breaks down all three options.
Quick Comparison
First, What’s the Difference Between These Three?
The keyword “network card” actually covers three completely different technical approaches.
Choosing the wrong one can mean spending more money without solving the actual problem.
PCIe Optical NIC: Old-School, but Solid
The oldest option of the three.
A PCIe optical NIC is an expansion card installed directly into a PCIe slot on the motherboard. These cards are widely used in servers and data centers, and there are plenty of models available on the market.
If you have a desktop PC or a NAS with an available PCIe slot, installation is straightforward.
The downside is obvious: you need to open the case, have an available slot, and deal with driver compatibility.
Windows and mainstream Linux distributions are generally well supported, but NAS operating systems can be more complicated.
USB 10GbE: Affordable, but It Has a Ceiling
USB-to-RJ45 Ethernet adapters are one of the most common choices for users looking for a simple upgrade.
The catch is that the “10G” number needs some context.
USB 3.2 Gen 2 has a theoretical bus bandwidth of 10Gbps. After protocol overhead, real-world LAN file transfer speeds are typically around 0.8–1.1GB/s. And if you have other USB devices connected at the same time, they may share the available bandwidth.
Latency is another consideration.
Mac users should pay extra attention here.
With Realtek-based solutions, some Mac configurations and system versions may deliver only around 400Mbps in real-world testing, while older versions have been reported to reach full performance.
Some models do not support macOS at all.
That means compatibility can become a bit of a gamble if you don’t check the exact product and system combination beforehand.
USB4 Optical NIC: A Different Kind of External NIC
USB4 or Thunderbolt in, SFP28 optical ports out.
When people hear “USB4 network card,” the first reaction is often: “Can an external network card really be that fast?”
That assumption is too early.
USB4 optical NICs and USB 10GbE adapters may both be external devices, but technically they are two completely different solutions.
The USB4 optical NIC solves a long-standing problem:
What if you want 25GbE, but your computer doesn’t have a PCIe slot?
For Macs, thin-and-light laptops, and mini PCs, 25GbE used to be difficult or impossible to add.
USB4 optical NICs open that door.
No need to open the case. Plug it in and use it. Move to another computer? Take it with you.
There is another advantage that is easy to overlook: you don’t necessarily lose the port.
A network adapter can use one Thunderbolt/USB4 port while providing another USB4 downstream port for additional devices.
Power delivery and daisy chaining can also remain available.
For laptops with limited ports, this makes a big difference.
The Key Difference: Latency
When comparing these three solutions, latency is one of the biggest dividing lines.
A PCIe optical NIC connects directly to the motherboard bus, with latency in the 0.5–1.5μs range.
A USB4 optical NIC uses PCIe tunneling. Thunderbolt and USB4 can carry PCIe traffic through a 40Gbps connection, resulting in latency around 2–4μs, which is still in the same general order of magnitude as an internal PCIe NIC.
USB 10GbE is different.
Solutions based on chips such as the RTL8159 use a genuine USB networking stack. Data goes through USB controller protocol encapsulation and processing, resulting in higher latency.
One important point: the exact latency numbers can vary depending on the hardware, operating system, drivers, and workload.
The difference may not be obvious when simply copying files, but it becomes more relevant in two situations:
- Latency-sensitive applications, such as remote desktop, streaming, and gaming.
- Multiple devices accessing the network simultaneously, where latency variation can affect overall throughput.
Put simply:
A USB4 optical NIC is essentially bringing a PCIe-class networking architecture outside the PC, while a USB 10GbE adapter uses a USB networking solution. They may both connect through USB, but technically they are very different products.
7 Key Parameters Side by Side
Here are a few points worth explaining.
USB4 Optical NICs Cannot Deliver 50G Throughput Across Two 25G Ports
This is one of the easiest things to misunderstand.
Two 25G ports theoretically require 50Gbps of bandwidth, while the USB4 upstream connection provides 40Gbps.
So the two ports cannot deliver 25G + 25G simultaneously at full line rate.
This is not a limitation unique to one particular brand.
The correct use cases for dual ports are redundancy—where the connection can remain available if one cable is disconnected—or network segmentation, such as physically separating storage traffic from office traffic.
Don’t expect the two ports to simply double the available bandwidth.
The “10G” on USB 10GbE Has a Practical Limit
The USB bus itself has a theoretical 10Gbps limit.
So even if the network interface is capable of more, the USB connection becomes the bottleneck.
That said, moving from Gigabit Ethernet to around 0.8GB/s can still feel like a major upgrade.
Dual-Port PCIe Optical NICs Can Really Run 25G × 2
PCIe 3.0 x8 provides approximately 8GB/s of one-way bandwidth, which is enough for two 25GbE ports.
If your goal is full dual-port 25G performance, an internal PCIe NIC remains the most straightforward choice.
Is 10G Enough, or Should You Go 25G?
Let’s look at the numbers first.
A 10GbE connection has a theoretical maximum of around 1.25GB/s.
After protocol overhead, real-world LAN file transfer speeds are typically around 0.8–1.1GB/s.
25GbE has a theoretical maximum of around 3.125GB/s, with real-world LAN file transfer speeds around 2.75GB/s under suitable conditions.
The raw numbers are more than twice as high.
But the bigger difference is headroom.
With 10G, a single high-speed workload can already consume most of the available bandwidth.
With 25G, multiple devices can share the connection while still having bandwidth left over.
For most home users, 10G is genuinely enough.
If your internet connection is around Gigabit speed, your NAS uses HDDs or a single SSD, and your main tasks are photo backups and media transfers, the storage system itself may not be able to feed more than 10G anyway.
But there are three situations where 10G starts to become a bottleneck.
1. All-Flash NAS
An SSD-based storage pool can easily exceed 2GB/s.
At that point, a 10GbE NIC becomes the bottleneck, while the storage system is capable of much more.
2. Multiple Devices Accessing the NAS
If two or three computers are simultaneously backing up data, transferring media, or working with the NAS, the available 10G bandwidth has to be shared.
This is where the extra headroom of 25G becomes valuable.
3. High-Bitrate Video Editing
Editing 4K ProRes directly from a NAS can already put significant pressure on a 10G connection.
With 8K RAW workflows, data rates can easily exceed 1GB/s.
At that point, a 10G network link can become the bottleneck, forcing you to copy footage back to local storage instead of working directly from the NAS.
So the decision can be reduced to one question:
Can your storage system, number of concurrent devices, and actual workflow consistently produce more than 1GB/s?
If yes, 10G may be holding you back.
If not, 10G can still be a very practical choice for years to come.
There is another detail worth knowing.
25G Can Be a More Future-Proof Upgrade
25G and 10G use the same general SFP28 form factor.
A 25G NIC can use a 10G optical module and negotiate down to 10G.
For example, the Lekuo DTB3F25 supports automatic 25G/10G negotiation on its dual ports.
This means you can upgrade the NIC to 25G first, then gradually upgrade your switch and other devices later.
Your initial investment does not have to become obsolete immediately.
That flexibility is one of the advantages of an optical interface over a traditional copper Ethernet connection.
Which One Should You Buy?
Now forget the specifications for a moment.
Let’s talk about users.
PCIe Optical NIC: Who Should Buy It?
If you have a desktop PC or a NAS with an available PCIe slot, and you don’t mind opening the case and installing a card, PCIe is still a very strong choice.
Before buying, check three things:
1. Does the bracket fit your case?
For example, a low-profile card may require the appropriate bracket depending on your chassis.
2. Is your operating system supported?
Windows and Linux generally have good driver support.
3. Is your NAS compatible?
NAS users should always check the compatibility list for their specific model.
For example, Synology DSM versions may have compatibility restrictions or network adapter whitelists, and third-party NICs can sometimes be recognized but fail to work properly because of driver limitations.
Before buying, search for:
“Your NAS model + NIC model”
It can save you a lot of trouble.
USB4 Optical NIC: Who Is It For?
This is the option for Mac users, laptop users, and mini PC users without an available PCIe slot.
It is also a good fit if you need a portable 25GbE solution that can move between computers.
For these devices, an external USB4 optical NIC can be one of the few practical ways to add 25GbE without opening the machine.
Mac users should pay particular attention to driver support.
With a driver-free solution, the NIC can simply appear as a new network interface in macOS after connecting it.
Also check the port on your computer carefully.
It needs to support USB4 or Thunderbolt.
A standard USB-C port is not automatically a USB4 port.
If your machine does not support the required protocol, the adapter may simply not work. This is a compatibility issue, not necessarily a product defect.
What About the Lekuo DTB3F11?
If you want an external optical NIC but only need 10GbE, Lekuo also offers the DTB3F11, a USB4-to-single-SFP+ 10GbE optical network adapter.
It is a lighter version of this approach.
Note: the DTB3F11 currently does not support macOS.
USB 10GbE: When Is It Enough?
If your budget is limited to a few hundred RMB and you simply want to move beyond Gigabit Ethernet, USB 10GbE can be a very practical upgrade.
For example, if your NAS already has a 10GbE port but your laptop only has USB, it can be an inexpensive way to remove the Gigabit bottleneck.
Going from around 125MB/s on Gigabit Ethernet to around 0.8GB/s can already feel like a completely different experience.
But there is one situation where buying a faster NIC makes little sense.
If your NAS uses mechanical hard drives, a single HDD may only deliver around 250MB/s.
Even two drives in RAID 0 may only reach around 550MB/s depending on the drives and workload.
In that case, the storage system cannot even fully feed a USB 10GbE adapter.
So before upgrading the network, consider upgrading the storage.
One More Group: Maybe You Shouldn’t Buy Any of Them Yet
If your internet connection is below 500Mbps, you don’t have a NAS, you don’t edit video, and your main requirement is simply storing photos and making backups, Gigabit Ethernet is probably still enough.
In that case, upgrading your network may not be the best use of your money.
Put the budget into storage instead.
So Where Does the Lekuo DTB3F25 Fit In?
[Colorful pencil-and-watercolor illustration comparing three network card solutions]
The Lekuo DTB3F25 is one example of the USB4 optical NIC approach discussed above.
It is designed to bring 25GbE connectivity to laptops, Macs, mini PCs, and desktops without requiring the machine to be opened or occupying an internal PCIe slot.
Its main advantages are straightforward:
- Dual SFP28 optical ports
- 25G/10G automatic negotiation
- Mellanox controller
- Around 2.75GB/s real-world LAN file transfer performance
- Windows and Linux support
- Driver-free macOS support
- USB4 upstream connection
- Compatible with Thunderbolt 3/4/5
- USB4 downstream port
- 60W PD power output
- Daisy chaining support
- Independent power supply
- Independent power switch
The two USB4 ports follow the same design philosophy.
The upstream port provides a 40Gbps connection, while the downstream port remains available for other devices.
It can provide up to 60W PD power output and support daisy chaining.
So when the network adapter occupies one Thunderbolt/USB4 port, you don’t necessarily lose all expansion capability.
The unit also uses its own power adapter, so the downstream power comes from the adapter rather than draining power directly from the laptop battery.
For comparison, the Sonnet Twin25G in the same general category provides only 15W downstream power.
Looking back at the seven parameters above, the DTB3F25’s position becomes clear.
For laptop and Mac users, it addresses several of the biggest limitations of traditional PCIe optical NICs: installation, device compatibility, portability, and downstream power/expansion.
Final Takeaway
There is no single “best” network card for everyone.
Choose PCIe optical if:
- You have a desktop PC or NAS with an available PCIe slot.
- You want maximum performance.
- You don’t mind opening the case.
Choose USB4 optical if:
- You use a Mac, laptop, or mini PC.
- You want 25GbE without opening the machine.
- You need a portable high-speed network adapter.
- You want to keep expanding your USB4/Thunderbolt setup.
Choose USB 10GbE if:
- You mainly want to move beyond Gigabit Ethernet.
- Your storage system cannot consistently exceed 1GB/s.
- You want a more affordable 10GbE upgrade.
And if your storage, network workload, and number of connected devices are already pushing beyond what 10G can comfortably handle, 25G is where the extra headroom starts to make sense.
The key is not simply asking, “How fast is the NIC?”
Ask instead:
“Can the rest of my system actually use the bandwidth?”
That answer will tell you whether you need 10G—or whether it’s time to move to 25G.
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