If you're wanting to box 10 on one pc, i7 is the best route.

Quad has 4 cores, and I7 has 5, I found each core could handle 2 wow's running, anymore added fps issues, and lag.

Ram really is important, but even with 12 gigs, I was fine at lowest rez, the more the smoother it will be. I have 24gigs now, and there is never any lag at all.

There is a section within keyclone, called CPU affinity, you can assign each wow to a core.

Also if you plan to buy a super pc, maybe turn your old one into your main pc , and run your tank on it. Keep your boxing pc clean too, all thsoe programs can boggle your performance up.