In which Tom doesn't understand networks

My model of the world is that, for most network-like purposes, computers are infinitely fast at computing and bottlenecked entirely by the difficulty of sending bytes across wires.

I now have two machines with 10GBASE-T network cards. I've plugged a cat6 cable between them, and done

ifconfig eno2 172.26.128.2
route add -host 172.26.128.1 dev eno2

on machine OAK and

ifconfig enp101s0 172.26.128.1
route add -host 172.26.128.2 dev enp101s0

on machine PINEAPPLE.

If I run 'netperf -H 172.26.128.1' on OAK I get 9411.48Mbits/sec throughput, which suggests at least something is running at 10Gb/s or so. Similarly 'netperf -H 172.26.128.2' on PINEAPPLE says 9402.15Mbits/sec.

But rsync between the 10Gbit interfaces on the hosts runs at the same 80Mbyte/sec that it did over gigabit ethernet and two switches. rcp is a bit faster (100Mbyte/sec versus 65), but I was hoping for high three figures.

OAK and PINEAPPLE both have fast NVMe storage which can be read and written at 2Gbyte/sec or so.

How can I get a file between these machines at at least half the wire speed? I feel I am missing some critical fact about networking in the modern age.