this is working router
ver 5.0RC5

CPU q9650
nic 82571 X 2

when the traffic < 550M , is very OK ，
wehn the traffic > 550m, the ping lost 2% packet , every CPU core < 100%。

wish improve it

show irq table plz

you can check /tool profile to see what uses your CPU power

try to disable RPS and assign active interfaces to different CPUs via IRQ load balancing

We have a pair of systems with i5 QuadCore with 8 Copper GigE Ports.
We can run Bandwidthtest from device to device and do 1Gbps in both directions without going over 2% CPU resource, and that is with connection tracking on.