OK. Just dual booted Ubuntu 64b at 2.639GHz. One way to check what the problem is to install it with a speed. If it's the OS itself, installation will pass easily but not the OS loading/functioning.
Flew through the install without problems. Booted too. But my GFX is not supported, working in 8x6 is horror and every other second, a certain application kept freezing up with low power load. Very buggy OS even at stock with TLB Fix.

I had to restart in the middle around 4 times and that kept destroying the HD/OS with errors. Next instance I had it sorted, 2.639GHz would always hang at loading Ubuntu at 135W AC load. That's 100% 32b stable speeds. Voltage upto 1.45V didn't make a difference whereas in 32b Linux/Windows, I ran it at 1.248V. But 2.626GHz would work error-free and it ran for nearly 9 hours now without fail. 64b LiveCD ran perfect and Memtest latest version passed 1hr before trying.

Gutsy 64b had higher idle and load power consumption.