Notes:

The blue line represents default system settings. Red line represents results after some optimization (see below). Interesting is performance drop at 1776 bytes with default settings. CPU utilization is pretty low even at max speed, not even close to 100%. These are optimization settings:

cd /proc/sys/net/core

echo "50000" > optmem_max

echo "10000" > netdev_max_backlog

echo "1000000" > wmem_default

echo "1000000" > wmem_max

echo "1000000" > rmem_default

echo "1000000" > rmem_max

Notes:

The blue line represents default system settings.

Red line represents results after some optimization was done:

cd /proc/sys/net/core

echo "50000" > optmem_max

echo "10000" > netdev_max_backlog

echo "1000000" > wmem_default

echo "1000000" > wmem_max

echo "1000000" > rmem_default

echo "1000000" > rmem_max