Hey there, I went from 3.2 to 3.5 GHz using the stock cooler, and got idle temperatures of 38C and full load temps at around 58C. Didn't want to push it above 60C full load temps, so I went ahead and bought a Cooler Master Hyper 212 and replaced the stock cooler. Now is OC'ed at 3.8 GHz, idle temps are about the same, but full load temps don't go above 50C.
Hope this kind of gives you an idea on how far you're willing to go on the stock cooler, cheers.