While the AS3 settling down helps, the burn in effect in the CPU of the higher mhz could real easy add more. The silver block perhaps just helped the CPU past a "hump" in it's ablility to O/C to the extremest levels. These seem by far the most likly to me in combination.
A very close examination of the base if you remount it will answer the deformation theory.
Or perhaps as noted above you should check on the state of the tides?
I'd suggest a posting to VR's list of uber O/C results is in order. Should be enough to push you up past a number of folks.