Gigabit Router Hardware Specs

[M. V.]

hi,

i want to setup a router-box with freebsd 8.0. with four Intel Pro/1000 NICs. 
the network i'm using router for, is a large and complicated network with high 
traffic almost all the time (up to 800Mbps for each of 4 NICs).  and route table 
may get large. so these are my questions:

1- first, i wanted to know what hardware specifications do you recommend (RAM, 
CPU, ...)?
2- about CPU, which feature is more important? Cache, Core-Speed, number of 
Cores, FSB, ....?
3- as a followup to my second question, which of these CPUs do you think is more 
suitable for me? and why?
    a) Intel Core2-Quad q8300 (2.50GHz)
    b) Intel Xeon e5405 (2.00GHz)
    c) Intel Xeon e5420  (2.50GHz)
    d) Intel Core-i5 540M (2.53GHz)

thank you.