I use the latest catalyst drivers and SDK 2.4 with success. On Windows 7 x64. I have no tried running linux, because I use this box also as my MS SQL Server.
OC switch turned off (Position 2): 670MH/s
OC switch turned on (Position 1): 740MH/s
From there, you can play with the overclocking settings a little bit in CCC, and get up around 800MH/s if you can manage the heat...
I ended up going w/ different clock speeds on my two boards (top board is set to a lower speed than the bottom board) to keep the heat down. Keep in mind that your situation might differ. I have no choice but to close the case and keep it positioned upright (or else my cat would jump in/on it).
I use GUIMiner. It's easy and fast to set up.