this is designed to fit in mini itx/htpc cases and still run a high end cpu for overclock. it probably isn't quite as good as a common cooler master hyper 212, it still is much better than the stock intel and probably the best low profile air cooler around. i see no reason why you shouldn't be able to get a decent 4.2-4.3ghz overclock out of the 2500k. you should download hwmonitor, intel burn test, and prime95. then you should just plug in a 42x multiplier and run intel burn test on maximum real quick for a few minutes to see what your temps are getting up to. as long as you are not going over 80c your good.
i guarantee you will be stable, but check the bios and what the cvid automatically changes your vcore voltage to and note...