I suspect the issue is with the game.
Update to the most current graphics driver. Each update will have tweaks appropriate to individual games.
If you want, go ahead and oc the 2500K. You can do a modest OC using the stock cooler. Just gradually raise the multiplier and see how you do.
If the OC does really well, then invest in a aftermarket cpu cooler and OC even higher. You can get a good one for <$30 or $40.
Out of curiosity, what does your windows experience index say?
its 5.9. my hdd is holding it back. i have a wd black caviar and i guess its not the best. everything else is 7.6 or higher.