I have the latest Catalyst beta drivers, APP SDK 2.9 and AfterBurner running on Windows 8.1
However, if I only enable one card (i.e. in Multiminer> BFGminer), I get 760KH rate and card runs cooler at around 39-45 Degrees.
UPDATE: I removed Crossfire cable and gave more breathing room for the cards. Unfortunately temperature is still a concern and 1st GPU is now only 300-320KH