Lasereth, I've got an Asus P4P800 mobo, with an "overclocking" option set in the bios. I can get 10% extra speed without much difficulty using that; My processor temperature will go up to some 55 degrees instead of 54... I simply didn't bother to keep it at such a "high" speed, because I couldn't notice any difference; I can't see if Need For Speed Underground is running at 80 fps or 85 (or whatever fps it's running at.)
I do agree that it's better to get a special (= better) cooler if you want to get serious with overclocking; I just don't agree that it's going to be a problem *that* quickly.