960 / 1250 is the highest so far that I didn't get artifacts with furmark but 3dmark03 failed.
900 / 1200 is what I play with right now and I think my power supply is giving me problems....either that or ty unstable power in this house, needs a big checkup.

Current power supply : Corsair 620HX
New power supply coming : Corsair 750HX (going to use an 8800GT for physx)