Well... If my memory don't fail me, WOW can take advantages with up to three cores. So I guess it won't really matter. AS usual, the GC will do the trick.
I'am on a phenom IIx4 955 (3.2 Ghz)+HD6950 : all the games run perfectly. (WOW with all settings at max runs about 40-50 FPS. Oh... One game...