This game is not going to be what Crysis was to PCs. Not even close, unless they're including settings far more demanding than what was in the Alpha.
In the Alpha, single 7970s/670s/680s were able to max the game at 1080p and have very playable framerates (35-45fps average depending on your clock speeds). My guess is that performance will be a bit better than that after Nvidia/AMD get a driver update out for the game closer to launch.
And theres so many gpu settings their adding in this time to where you can cut down if need and still have a great experience. http://www.evga.com/forums/tm.aspx?high=&m=1808431&mpage=1#1818202