Folding on an overclocked Sandy Bridge question!

Hi guys,

I currently own an Intel Core i5 2500k on a DZ68DB motherboard with which I fold proteins 24/7 with Folding@Home. Since it uses all cores at 100% all the time, overclocking it would be a big benefit. However I have tried many combinations of overclocking options on this board and managed to make the core multiplier go from x33 to x47 (which makes my processor work at 4.7 GHz), but this only happens for, in average, one minute before the processor reverts to x33 and stays this way from then on.
My dad wishes to change his computer, so I am thinking of this: Give him my current motherboard and buy an ASUS or ASRock motherboard with better overclocking capabilities than Intel's. However, I am not sure if the fact that it reverts to x33 after a minute is a problem of the Intel mobo, or it's an inherent behavior to the processor that happens regardless of the motherboard used. Being able to fold at x47 the entire time would justify me buying another motherboard and giving mine to his, but if the mobo makes no difference I'd rather keep my current board and buy a cheaper one for him instead.
Heat is also not the issue, as I have a Hyper 212+ heatsink and the reverting back also happens at lower multiplier settings.

So, is anyone here with a Sandy Bridge processor able to constantly fold, or run prime95 or other processor stress tests, at high turbo multipliers without it reverting back?

Thanks!