Spend the extra $5 and grab this: SAPPHIRE Radeon HD 7850
Granted WoW seems to run better on Nvidea cards, but since the 7850 is a stronger card, it will more than make up for the differences. The 7850 can also overclock to 7870 levels which are on par with the 570 in performance.
Other than that the build looks solid with the addition of a CPU Cooler. I have this one and it works fantastic in keeping my 2500K cool @ 4.1ghzCOOLER MASTER Hyper 212 EVO