The difference is the primary base clock speed of the chips. The faster (bigger) the clock, the faster the CPU can process data. Most users, that use their PCs for websurfing and basic office type programs, wouldn't notice much difference between the chips, you really only need higher clocks if you do higher end gaming or things like video processing. So, it comes down to what you plan to use the PC for, as well as the other components in the system (no point in putting a higher end chip in a system that is made up of otherwise inferior parts that won't keep up).