Okay, what about case temperatures? Pixelated artifatcs are the cause of a.) an on it's way out g/card or b.) high temps due to overclocking and/or ambient temps.
Also, if you have Anti Antialising and Anisotropic Filtering on try putting it off (I doubt if this is the cause)
You can also try ATiTool - it has an artifact scanner and if it still shows the same results you might consider the probability of your g/card being kaput.
Hope this helps!
