You should be fine, but, just curious, why do you need it?
My single 670 can max out almost any game at 120fps. Spending $400 to turn on supersampling in the Witcher 2, to see no benefit at 1080p, seems kind of silly.
(And if you're playing on three monitors, I'd advise going with the 4GB vram versions of the card, just for safety.)