Two GTX 280 are enough for Crysis
At 2560x1600 2X AA
If you are hoping that a single GTX 280 will get you to more than 1920x1200, don't kill the messenger as I have to regrettably disappoint you.
Nvidia claims that a single GTX 280 will be enough for Crysis at 1920x1200 that is a standard resolution for most of the 24 inch LCD's.
If you have 30 inch display that supports 2560x1600 you will need two GTX 280 but again we heavily suspect that you won't be able to play with FSAA 4X enabled.
This would be too much even for two GTX 280 cards. It becomes ridiculous as two of these cards combined have 2.8 billion transistors and they will still not be able to bring Crysis to its knees. The best you can hope at 2560x1600 is 2X FSAA with these two cards.
We’ve had a chance to play Crysis with a single card and we can tell that 1920x1200 FSAA 4X with beta drives bring the card to its knees. Ouch, isn’t it.
As expected, 1 card isn't enough to run it with 4xAA. Bandwidth matters.