yes, HUGE difference is right. THe only time you don't notice an upgrade is if it is above 500 mhz at stock speed and only overclocks to 150 or so higher. You need a huge overclock to notice any difference. If you just think about it, a 100 mhz to 200mhz overclock was a very, very substantial difference because it was a 200% overclock. But 500 to 600 is only a 120% overclock. It's pure math when you think about it. I have a p3 700 and i have it a ghz right now, but i notice basically no difference between ghz and 700. I think i have lost my enthusiasm with overclocking.