What BIOS update?

I have a P5B Deluxe. Bios versions 1004 and 1101 didn't hold on my overclocking settings. Version 0910 was stable for me. To revert back from newer to older bios, you will need an early AFUDOS version. I will advice to check version history of all released bioses after yours. If one of them holds a vital update for you, then go for it. Install your system. Overclock it as needed. When you're happy with it, update to latest version. If every thing is fine, keep it, if it s*cks, get your hands on an early version of AFUDOS (http://www.box.net/shared/4kyjpc79qu credits to xbioses for the upload) and reinstall an older one, check it...

Good luck

See my rig in my signature
I don't own an E6600, but:
Follwe the pinned guides here on how to overclock your C2D
Fix all volatges and disable all voltage/speed..., lock DDR to 1:1
Increase FSB and test some few mn with Orthos.

When you get errors: 2 choices
- satisfied with the speed: decrease FSB some 4-5Mhz and Orthos again, when no errors for some few mn, go for a rock stability test over 16h (8h for medium stable)
- Not satisfied: increase vcore

Then tweak your RAM

vFSB/vNB/vSB/vICH shouldn't be raised below 350-400 MHz, but you can put them on the value before the red setting (on ASUS MB) so they are out of the equation. Once you reach your speed, decrease them and check stability

Check the posts here, there are so many discussions / expieriences

And don't forget: each CPU/MB has its own overclock potential