I hate to tell you but no card, not even 2x 8800GTX will run that resolution smoothly with new games. 1920x1200 is looking to big for DX10 gaming because of the poor performance, let alone 2560x1600.
And being a owner of a syncmaster, they have a ton of input lag. I can only imagine with that size of screen. The bigger the screen, the more input lag.
Two words, Stay away.