Not quite sure how to notch back the overclocks myself. One thing I did notice though, is I had this same problem happen for the first time in another game. It happened about 3 minutes after I turned AA up to max.

I solved this problem on FF by keeping my AA at the normal, and also turning down Ambient Occlusion I think it was.

Its funny though, because I am not overheating when the computer seizes up. Could this be a driver issue?