brand correlates with build and cooler quality along with customer service quality in my case.
for your budget, you got a good deal of choice to pick from the GTX660, GTX660ti, 7870, 7950, or a 7970/GTX670, with the right deal. granted, the 7950/7970/660ti/670 are overkill for WoW, but i guess you can try to future-proof it for future expansions.
there are mainly 2 version of the 7970; the 7970 & the 7970 Ghz edition, which is basically a 7970 with a higher base memory & core clock. the article is comparing performance between the old AMD catalyst driver and new.
you'll be waiting for a good while for the 8000 series. no news when it's coming out. with Cyber Monday coming up, you may even find a crazy cheap deal on a 7970, and they're damn good enough to last you a few years before you need an upgrade, so consider that.