Odds are if you're using a 580, then you don't want to buy ATI regardless.
Not at all, I look at the facts and be realistic. I don't honour one brand over the next. If this was churning out acceptable framerates @ 2560x1600 I'd grab one.. It doesn't though - and in reality it is nowhere near worth the upgrade over a 580. The performance boost it does have over the 580 @ the lower res would go unnoticed.