5870 is pretty much the only choice right now if you want to get 60fps maxing out crysis.
2 of them in crossfire would be fine for 1920x1080 maxed and with 8xaa, but if you're planning on 2560x1600, a 3rd will likely be needed (though it may just about squeeze through, i havnt even tried the game at that res)
im assuming you have a beefy proc too? you'll need and i7920/870 really, if you want 60fps maxed.
i have all the requirements needed for the cards i just needed to know the cooling ide need for crossfired 5870s. im planning in 6 fans and a cooler master case the limited edition warfare cooler master case. to be exact
that should be fine. despite their power, the 5870s run fairly cool. they vent most of the hot air outside the case thru a backplate vent, so as long as you have relatively good airflow it should not be an issue.