What about overhead? Can you truly do 10Gb/s networking on a 10Gb/s USB port? Would having such NIC on a 20Gb/s USB port not result in higher speeds?
I am of the opinion that 5Gbe is a much more sensible speed for a laptop adapter right now as it uses half the power and can obviously run full wack on 10Gb/s USB so you're looking at like 5Gbe vs ~9.4Gbe.
At distances where Cat.6A is even an option the demands on the fiber are very low. And it uses less power than the BASE-T PHY. The cable at least without integrated power is very thin as well, unless you can't respect it enough to not kink it, in which case you'd want a thicker one just to prevent you from being able to break the fiber.
And you get much better future proofing with SMF. And if you do need a long fast run, SMF is what you want.
How do I power an access point with fiber? Ok we add an AC wall socket to the ceiling but now we need a 'brick' to convert to DC. How do I remotely hard reboot an access point if it were to crash?
Fiber termination requires a fusion splicer and a trained engineer, sharps box etc. The power socket needs an electrician. It's just such a nightmare in comparison, install is going to be more expensive, longer to fix faults, less flexible to move a socket etc
So the their maximum speed is approximately 9.7 Gb/s.
Then for Ethernet there is a protocol-dependent overhead, e.c. depending on whether TCP or UDP is used, and depending on whether standard packets or jumbo packets are used.
The TCP overhead can reach in the worst case up to close to another 3%, reducing the achievable TCP throughput to around 9.4 Gb/s.
The USB frames add some extra overhead, but it is normally not important in comparison with other factors that can reduce the throughput.
All that a 20 Gb/s USB port can do is to reduce the overhead of the USB frames, but that is a negligible improvement. Using jumbo Ethernet frames (which are 6 times bigger than standard frames), if both ends support them, is likely more useful for increasing the throughput, than using a 20 Gb/s USB port.