Since OPNsense got newer drivers for the 10GbE than FreeBSD 13 do you have any idea when they get included in FreeBSD? I couldn't find anything related to this driver. But then I may just looked at the wrong place.I did compile a custom FreeBSD stable/13 kernel with the code diff for the axgbe from OPNsense and it works well. Having it upstream would of course be even easier.
What I did see though is a difference of cpu load when receiving packages. The cpu load while receiving (iperf3 -R) is about 2 to 3 times higher than sending on a fresh installation of FreeBSD 13. Using iperf3 with one client (-P1) and on the other end is an Intel X520 I can max out the 10GbE easily.Playing around with net.isr.dispatch, net.isr.maxthreads and net.isr.bindthreads didn't change much.
And now to the completely off-topic: The Linux shipped kernel 5.13 and also the lastest 5.17-rc2 do not recognise the AMD 10GbE interfaces. Are you in contact with the developer(s) from AMD and have any idea what the plans are in regard to the Linux kernel and the amd-xgbe driver? From the OPNsense axgbe code diff is seems like it would not be too much work for the developers to have it working on Linux.