i'm using the dual X version, it's FAST @ 1080p. now bear in mind that the 285 is already out with newer feature sets you can try to consider that card as well.
also i've been advocating that radeon cards are "broken" without radeonpro. this 3rd party software adds dynamic vsync. (try playing ac4 blackflag with DVsync on and off).
what version of sapphire are you going with?