For maximum WoW performance you want 2GB ram, a Raptor, and a 7600GT.
Anything above that is just great, CPU is pretty irrelevant as you'll get the same performance with a a64 3000 as with an fx57 in wow.
Intel core I7 920
6GB OCZ platinum 1600
Samsung 1TB F1 Spinpoint
Samsung SM2443BW 24"