Could it be that Phenom limits current draw at a certain level? That would explain why it's so sensative to vcore tuning. Maybe if that's the issue there's a way around it (like drive strength tweaks with RAM).

If the current draw is indeed limited (in some parts of the CPU?) that may also explain why some day the CPU is stable at certain settings, the next it's not and the day after that it's stable again. A max. current limitation means the CPU is a lot more sensative to temperature changes.

To remain energy efficient AMD has every reason to limit current draw in (parts of the) CPU. I heard that the 9500 often clocks higher than the 9600BE. Maybe AMD lowered the roof for current draw to prevent people damaging the CPU as the BE was a rushed-out product using a very new architecture.

Just some wild theories....