Then, download Prime95, this will stress all 4 cores of your CPU to 100%. Do this with CoreTemp open and post a screenshot, or the temperatures here. Just so we can see how much headroom you'll have.
I'd recommend taking a look at the idle temperatures first, and then post them here before you start stressing the system.
I would but i haven't assembled my comp. yet. I thought I'd plan ahead so as to get the most out of my PC, and so i could buy the needed extra's before i completed the assembly.
even computers with the exact same specs will overclock differently, theres just too many factors contributing to how high you can overclock to realistically plan ahead an overclock. overclocking a Q6600, you can safely bet on 3.0ghz but past that depends on a few different things, like voltage, cooling, motherboard, ram, northbridge...