I run a 7970 (which was rebranded to the 280X, no difference other than firmware) and it runs triple 1080p Eyefinity in modern games fine. Its going to depend on how sensitive you are to FPS, but its definitely playable.
Awesome! Thanks for that, it made my mind up. I wont be playing too many intensive or demanding games. But I'm glad the card will be able to handle it fairly well!