My 5-year old case has a foot of clearance. Any $50 case also has enough.
50 dolllars or 250 dollars, if there is not 11 inches of clearance it don't fit.
Its a big card. Its longer than ATI's past dual gpu 4870x2. They probably did in part to fit a bigger cooler. The 5850 is over a inch shorter, but runs at a lower mhz with less SP's.
5870/5850 11/9.5 http://www.tomshardware.com/reviews/radeon-hd-5850,2433-2.html