just asking how much overclocking would a, let's say a medium or high end CPU, Intel or AMD, get on a stock cooler and stock voltage (or a little voltage boost) I've read that some people got their CPU's OC'd to a nice "speed" on the stock cooler, which is usually not that good other say that it is not possible at all and obviously not recomended with the stock cooler
to add on this question another
for a user that uses the PC only for gaming (1080p maxed out), (including CPU intensive emulators DOLPHIN, PCSX2, plus PC games StarCraft II, Bad Company 2...CPU intensive is what I mean), browsing the web, watching HD movies, listening music, using MS Word, NOT doing any picture/video editing, no 3D design, no programming etc...would overclocking of the CPU be needed (let's say it's a decent CPU), what improvement would I expect, I know it's a must have for dual/3 way GPU's for not bottlenecking........I think you got the point of the question
P.S. i know very little 'bout OverClocking (obvious)
Most CPUs can be overclocked at least a bit - to a "nice speed" as you say - on stock cooler. But any stress or serious OC attempt typically warrants an aftermarket heatsink.
To your second question - it depends on the program and your system. More specifically, where the bottle neck is in your system for the given program. For example, if you're running a GPU intensive game on a high end CPU but a mid tier card that can't keep up, you could potentially Underclock your CPU and not notice a difference. Therfore OCing your CPU in such a case would also bring very little benefit. Money or time spent OCing is better invested in such a case in teh GPU.