I am on a tight budget, I have a P5K and i don't which cpu will give me best OC performance. Any advice?

If you're on a tight budget, the Q6600 will be more than enough. You can easily do 3.2GHz, which should be more than enough for whatever you do, probably.

Whats your budget and how do you use your system.

If not video editing and such a good ol e21xx series will OC 3.0-3.4 pretty easy, possibly more with a real good cooler. e2180 is probably the best buy on newegg right now. I have it running 3.0 stock cooling on 2 machines with P5K SE.

Q6700 and Q6600 will most likely hit the same FSB without extreme cooling.

Lets say you wanted 3.2 the q6600 will need a higher FSB which will actually give you better performance bandwidth overall.

I vote q6600 if you need video editing. If not the 21xx is the ticket.

i already have a e2160 at 3.25ghz right now with stock cooler, can a q6600 go past 3.6 with a P5K and a TR Ultra-120 extreme?

It would be Iffy? Depends on the chip. If you dont multitask heavy or have apps that utilize 4 cores the upgrade is not going to be noticeable.

Maybe a new GPU, HDD, LCD would be a better investment this round.

I also agree with Roadrunner. Unless you really need a quad for heavy multitasking, stick with what you got.

I just need a cpu that will last me 2 years and i think a OC Q6600 will do the job.

Might as well save up for the new CPU lines coming out in January. Intel and AMD are launching new sockets and such.

i was going to but after this quad core i am probably gonna save up for a nice laptop for out of town studying.