I am currently overclocking my e6600 to 3.06 on an Asus P5B Deluxe motherboard.
Thinking of upgrading my cpu but don't know the most cost effective one to get (quad or dual). Want to keep my p5b (bios 1236) as accounting (the wife) will not approve both motherboard and cpu as I am also upgrading to an ati 4870 512mb card from an 8800gt. I us the computer for gaming video encoding and general all-round use.
Go quad, I would go with the q6600 if money is a bit tight. but if you can really afford it go with the q9550. With the q9550 it's much easier to hit the 1600mhz fsb then with the q6600. While I'm fairly sure you board supports the newer 45nm chips you may want to double check.
Yes it does support the 45nm cpu's with the latest bois 1236. However I have heard of problems with the e8xxx cpu's having problems with 4gb ram or more installed. Suppose to be a 1237 bios update to solve this, but can only find it for the p5b deluxe wifi board. Don't know if the p5b deluxe and p5b deluxe wifi 1237 bios is the same for both motherboards.