I currently have my i5 750 overclocked to 3.2 using the "CPU Level Up" option, but if I change it back to default and enable Intel's SpeedStep (along with Extreme Phase) I can get my cpu up to 4 GHz with stable temps (50 - 60s).
My question is that if its worth it, I am playing games on my rig btw. I'm just not entirely sure if it would actually do anything when I play a demanding games like Fallout 3.
PS. I've tried it out and I'm still not sure if it does have any effect on the framerate (even after checking the before/after rates lol)
It will have an effect on the frame rate, but you won't notice a change above 30 fps anyway, from 3.2 to 4 it might go from something like 30 to 35 but then it might not, each game is different.
It depends whether you feel comfortable at 4ghz or whether you would rather lower it to be "safer", and to know whether it is worth it, check what your idle and peak power draw is at both clock speeds and mesure both figures against performance (probably using a synthetic benchmark), you might find it is worth keeping it at 4.
Also when playing games it is mainly the graphics card(s) that will be put under the most pressure, if you have overclocked your card, then this will also affect frame rates. TBH it doesn't sound like you are having many problems with it anyway!