With 45nm ~1.60 vPLL is the soft limit, so keep it under that, preferably under 1.57v

Pretty sure NoGuru used a UD3P for those clocks, its widely understood to be the best board for overclocking quads.

Raw CPU stability (Prime95 small FFT's, LinX) is pretty easy to do on most boards up to a point, its Prim95 large FFT's and long blend runs that really expose instability. You may find it tough to pass especially with 4GB+ ram installed. You would want to run a few hours large FFT's or blend run to be sure you're stable.