forget the new gpu, your 560ti is certainly good enough. Wow hardly makes use of the gpu. You generally hear that intel is better for wow, but it is much more expensive. I have very often 10 accounts running and i hardly use 30% of a geforce 570 vanilla.
@Copyleft:
i also have a 2600K, but i really don't understand how you come to 20% cpu usage with 20 wow! With 10 wow, on stock clock (3.4Ghz) i am usually between 70-90%. I don't think that your light oc could make that much a difference. I know, i have tried it. I thought it was not worth the more than 20% extra power consumption. And I also have 16GB ram of which I never use more than 10.