I'm far from Pro ATI, but I must say that my Radeon 5850HD Black edition has been running very strong for several years. It still plays all high end games @ max settings. My latest is BF3.
Those SFF dells are a nightmare for several reasons. We had to stop buying them. Those cards are likely burning out from one of the major issues with the SFF's. Terrible heat distribution, and other than ample fans.