i've gotten crysis 2 running smooth with an i3 so you should never have a problem.
That's... not possible. Crysis 2 barely has trailers out. You mean Crysis: Warhead?
Crysis: Warhead runs better and smoother than the original Crysis, that first game was just not very well implemented tho it looks great. I have to think at this point in time it would be very unlikely that Crysis 2 is going to crush modern GPUs. A 5870 should definitely do high settings. Very high tho? Hard to say. Hopefully the optimize it like Warhead but for now we just have to wait.