Interesting thought... what multiplier was your Sandy running at? Would the bios then attempt to run your cpu with this multiplier after you swapped cpus over? And was this enough to change the cpu?

ie. Was the mobo's bios forceful in telling the cpu what multiplier to run at, and the cpu chucked a hissy-fit and started carrying on like "fine, from now on, YOU can tell me what multiplier to use... Im sick of doing all the thinking for myself!! How do you like that, Mr. ImAFussyBiosWhoHasToHaveMultipliersHisOwnWay?"

Or something like that.