Intel Core i7 950
4GB RAM
Windows 7 64 bit
ATI Radeon HD 5700 Series
Hitachi HDD 2tb 7200rpm 64mb 6gb/s
Ok we have several similarities. Separate HDD for the game, ATI graphics card, 64 bit OS, intel CPU.

What catalyst version are you using? Also, go to performance -> AMD overdrive, and can you tell me if gfx overdrive is enabled? Many card do this by default.