How much kpps mt can provide on P4-1.7 256 DDR for simple routing(no queues, ~65-70 firewall rules)?I have read one forum and there many ISP write that mt can provide less then 10 Kpps.Is it true???BSD, for example, can provide 30-50 Kpps on this hardware…sorry for my english 
24 kpps even on 266 MHz RouterBoard. This was without firewall, though.
Alex, P4/1.7GHz has so much power that you will never use it.
You didn’t say how LARGE packets do you process - there is difference:
20000 packets/second, 80 bytes long
20000 packets/second, 1400 bytes long.
Definitely buy Gigabit NIC, which OFFLOADS CPU and bus from processing as much as possible, good examples are Intel Gigabit adapters (but not the cheapest ones). Take Gigabit NIC even if you don’t need that speed.