Yeah, they’re mostly used for overclocking. If you have RAM that can handle higher clock speeds, you can increase the bus speed and overclock your computer that way, since most processors are now multiplier-locked.
Thanks. I just checked the Corsair website and they list PC3200C2 for the “Enthusiast”, PC3700 for the “Overclocker”, and PC4000 for the “Extreme OC”. Well I am not planning on overclocking the 3 GHz chip so it shouldn’t matter.