Back to the case, keep in mind the GX2 is very long, and won't fit in many cases. You'll need something with plenty of depth to be comfortable. I don't even believe it would fit in a P182 without removing the upper hard drive rack - obviously in a cheap case that rack would likely not be removable.
Regarding 'would it run Crysis', the answer is yes. How well is another matter and is largely dependant on the resolution you'll be running at. Crysis doesn't scale particularly well with multi-GPU (SLi/Crossfire) cards/set ups. For instance, even at a GPU crushing 1920x1200 at high, it still only achieves an average of 40fps according to Anandtech (not a source I'd normally check, but it seems OK). It's hardly much less than the 43fps at 1280x1024. Then again, 2560x1600 gets a massive 8.9fps. Crysis is very, very poor technically.