as you know the stock cooler isent good for overclocking. but that doesent meen that you cant overclock.
do you know how to overclock?
if so.
it is just finding a speed that doesent make the cpu tempature go to high.
i will recommend cinebench to tjek if it is getting to hot. also to see the difference in performance.
i think you will be able to get 3,5. might even higher if you do it right.
i had my core i7 920 at 4 ghz with stuck cooler.
howerver in game when my room temps are high, it whould be way to high temps.
it bsod on me twise in 1 week because of overheating, so i downclocked it to 3,6. no problem there.
you can also make the overclock unstable. like if the volt isent right, or if you have some cpu fetures set wrong.