hello friends, it's been a while..
I just tried Windows memory diagnostic (WMD) (from Hiren's boot CD)
it says that WMD could not process the system memory map because of deficiencies within WMD, not the computer.
Reported error was: THE MEMORY MAP CONTAINED RANGES THAT EXTEND ABOVE FOUR GIGABYTES.
(and hence the test will not be able to test all the installed memory).
BTW, you're saying that "thermal" and "processor" modules were those that caused the machine to reboot Wouldn't it be the same issue with an x86 kernel(s)? I'm not sure why would that specific modules caused reboot issue only on an x64 kernel? The above mentioned reported error from WMD is more likely our way of light. Something is wrong with 'the memory map' inside of BIOS , like there's no border for the fourth GB or more precise - 4096 MB.
One more perhaps less important thingie: try to run GoldMemory with AUTO (instead of BIOS) memory addressing. With BIOS it's ony ~3 GB's, and with AUTO - full 4 GB's but it just hangs the app like expected xD
On the other hand, MemTest86 is able to test the whole 4 GB's.
If you both have some spare time - try OpenSolaris 2009.06. It must be using PAE but i'm confused why it is enabled by default, since there are known issues with drivers and PAE.