Same thing is happening to me. I got like 8k on the benchmark using mobility radeon hd 5870 crossfire. I can get a solid 60 fps for awhile, even if crazy fates....nothing even changes in the environment around me and I drop to 16 fps....I already posted about this on the forums awhile back. Uninstalled and reinstalled my drivers, got the 13.8 beta drivers....still nothing =/ I dunno what it is.