Have you run any diagnostics on the card?
I'm not sure but i think programs like RivaTuner allow you to run low level diagnostics on the card.
Also run something like 3Dmark and compare your results online to se if they are below normal for your hardware setup.
Intel core I7 920
6GB OCZ platinum 1600
Samsung 1TB F1 Spinpoint
Samsung SM2443BW 24"