A decent cpu cooler makes a huge difference.... the Xigmatek I have made a world of difference with the cpu temps. You also really need northbridge cooling to get decent overclocks with the P7N (at least on mine anyway). Without the 120mm side case fan my rig was very unstable when trying to overclock past 1450 FSB. With the side fan, it easily does 1600 and its rock solid. I also have to give the NB lots of juice. At 1600 i need at least 1.425 to be orthos stable. I give it 1.45 and as long as its not 100 degrees outside, temps are under control.
Try increasing FSB term to its max amount and giving SB some more volts. And loosen up your memory timings so you don't have to worry about that being an issue and then just raise them once you get it stable.

Of course, if you've done all this already, then you just may have a dud of a cpu and/or board. It happens.