I'm getting around 24.8 from a 290@1125 and 4.3 from a 7750@950
Mem clocks are default. I can't seem to get anywhere near the 28MH reported. Running with 13.12 drivers and 14.3b ocl libs.
Try -w 64 -X 105
I was at 8, W at 64. Windows with 13.12 drivers did get me the 27.something MH/s Thanks for the xintensity advice.