Regarding the throttle back functionality:
P3 CPU's - when they overheat, they shut down the PC (P3 survives)
P4 CPU's - when they overheat they throttle down by reducing the speed till they come between 60-70 C
Modern Athlon's on modern motherboards (last few months) have a protect switch which shuts down the PC when the processor core reaches to high temps - but this is not implemented in the processor.
And, high voltage (10-15% over default voltage) without proper cooling (water...) probably will kill your proc in few months or earlier, since in the core a process called electron migration will happen and the transistors will loose their functionality.