Ya that BSOD is 99% of the time Vtt, but it can be Vcore too but not very often.

No need to switch CPU's, they are both the same anyway minus locked/unlocked multipliers and the $1000 price tag, they will both overclock to the same range.

So just overclock that one to 4Ghz and leave the lesser CPU in the machine you plan to run at stock.

Try disabling two cores so you can run dual core, then see if you can get 500 FSB under control.