I have 3 Sapphires running 975core/600mem/stock voltage and they all crank out 292-295mhash/s. For some reason when I drop the memory clock lower than 600 the card locks up. I'm using MSI AB.
I did some more tuning with MSI AB on each card individually instead of the "synchronize like gpus" setting. I found that I only have 1 card that won't go below 450 memory without crashing. The other 2 will easily go down to 300. The core clock on the 3 has been adjusted to 1000mhz. Actually output now is 309.6mhash/s using VECTORS BFI_INT FASTLOOP=false AGGRESSION=12 WORKSIZE=256 -k phatk inside of GUIMiner.