I have that same processor running at 3.9Ghz. I also have 1150Mhz RAM which gives me a wider range of FSB numbers. Actually...I have a P5N motherboard as well.
I don't have my computer with me atm, though, since I'm in Iraq, but I'll try to remember what I had going.
First, power on the computer and enter the BIOS screen.
FSB-440~
core multiplier-9
(or try FSB 460, core 8.5)
Vcore-1.45(after getting it stable, if you do, lower the voltage as low as you can while maintaining stabilty)
The RAM speed is difficult, as we don't share RAM. There should be speeds in there you can choose. I don't remember what the option is called. Anyway, set the voltage to 1.9v, and try it at about 900Mhz. Keep in mind, the speed of the RAM depends on the speed of the FSB.
Good luck, and keep an eye on your temperatures. Don't let the cores stay above 75c.