Depends on the CPU and mother boards. Some CPUs are more receptive to overclocking than others.
What he said. Though, unless you consider and treat overclocking like an extreme sport (yeh there are overclocking nationals!) it really ain't worth it. I would just buy a faster system. The amount of futzing and putzing you need to do is disproportionate to the end results.
I always tell my clients it is easy to upgrade to more functionality, like adding in a digitizer or a printer or expanded networking capabilities, yepsticks, ghamepads, multi-monitors..
It is much more difficult to upgrade for increased performance speedwise. Usually, you want more FPS, so you get a new supha-doopah graphics card, well, that demands to be fed, now you need a new cpu to push data to it.. Heheheheh - now you need new memory and a motherboard to match the cpu and tie it all together. Hopefully, your power supply is good enough to handle an overclock or an upgrade. And your case sufficient to handle the extra heat.
*I* personally view the mobo/cpu/gpu combo as one. And all three components generally should be upgraded and swapped all together all at once.
Folks that often get a wow-whiz-a-bang performance increase by changing a "single" one of those components separately are lucky. And even more likely, they had an unbalanced system to begin with! An unbalanced system which is now correctly configured and working.
I tell you it's a racket out there, the graphics card industry just loves upgraders!
