I be honest to test rigs to see if the OC is safe I prefer to know it is completely stable so I do 24h tests before I am happy with the settings and leave it be.
As for the voltage back when I was reading on how to overclock I learned Voltage and Heat killed hardware. Voltage was one of the killers, but it also generated heat when you apply more of it. So handling the temps alone weren't the only concern the voltage is also a concern, and is also directly related to heat so try to keep that in mind. Hope that made sense.
Short way to look at it: Increase Voltage = Increase Heat
Increase Voltage = Less CPU Life
Increase heat = Less CPU Life
Increase Voltage/Heat = Even Less CPU Life