It seems that whenever I take my 5900SE over ~450/750 with Coolbits, I get a worse benchmark in 3dmark 01se even though no artifacts are cropping up... Has anyone else run into this odd phenomenon when overclocking the 5900 series cards?
You can get speed decreases by overclocking if the component(s) are not sufficiently cooled. Try opening the case, adding a fan pointed directly at the card, and check your results.