Orthos or Prime95 small FFT's will tell you if your cpu oc is stable.
The blend test will tell you if you need more NB voltage/tweaking.
*Fully explained to me last night *
What are your current voltages..? I've never been past 3.8 but I'm sure someone will come along and be ready to help after seeing where you're at.
So: what fsb are you at?
List your volatages.