My is on 35-45 Even cities get a bit low, and when other players (more than 15) are appearing. but It's nothing for PvP, I'm only doing Instances so for this it's enough , but for 300 € I get a Second one, a good one should start @ 500 or something, to run all by itself. And depends on how are you stting them up, Are you using 1 Monitor, then you don't need much performance for it, because you see only 1, if your running 2 Monitos and setup your maximizer like 1 / 4(4 on second in "Split Screen") then you need more performance because you have displaxyd every wow client.

RAM is the Most Important thing. When your running Vista get so much you can it helps you, believe me^^ And you should get a Quad core or at least a dual core 1 core is a bit weak for multi tasking.