I don't know how well this will translate to your setup, but here's my config:
i7 920 @ stock
Intel x58 mobo
4GB DDR3 1600
2x 8800GTXs (slightly downclocked to help keep them cool).
I'm able to play the original Crysis in DX10 (all in-game settings maxed, and all driver control panel options maxed for highes possible IQ- including SLi 32x AA) and still have perfectly smooth gameplay. How? Well, I'm gaming on a 17" (15" viewable) LCD I pulled from recycling at work. It's max res is 1024 x 768.
But still, with all that eye candy even at that low of a resolution- I'd wager your current cards should be fine. Maybe not with SLi 32xAA but they'll still get the job done.
If not, I can guarantee two 5870s will.