This really depends on the board doesn't it? I know Asus board OC well on auto voltage...
Well nothing is set in stone these days!
Especially since some have BIOS flashed their original Sandy Bridge M/Bs with Ivy Bridge BIOS flashes.
Which is great for Ivy but sucks for Sandy!
If you are getting contrary results, what does CPU-Z report that your clock is doing under load?
If it's say clocked to 4.7ghz under stress testing have CPU-Z running and watch the clock speed and see if it changes?
If it does not change, please post your specs?