Having just been migrated (by hetzner) from the e1000 to the vtnet driver, I found that some network slowness.

FreeBSD and vtnet drivers

It all might come from certain driver issues FreeBSD is (unfortunately still) having with vtnet. What helps for the time being: (help) debug and submit a patch, and/or set in /boot/loader.conf the following:

hw.vtnet.X.tso_disable="1"
hw.vtnet.tso_disable="1"
hw.vtnet.lro_disable="1"
hw.vtnet.X.lro_disable="1"
hw.vtnet.csum_disable="1"
hw.vtnet.X.csum_disable="1"

Fun fact: Running wireguard works like a charm. Full speed, no issues. Cause that was the only real load-test I did after the migration. But once TCP packages leave the system over the network (driver), ooh boy.

Thanks to this blog post for hinting into the right directions while reading up on something very unrelated.