I've oc'd this CPU to 4.5. Increase the multiplier in BIOS and take it up to 4.2Ghz first, then boot in and run LinX or Prime95 to check stability. If it crashes or fails the run then go back into BIOS and increase Vcore by .025v, boot in and try again, repeat until it passes the stress test, then go back in and increase the multiplier again to 4.4Ghz, just keep repeating these steps until you get 4.5Ghz stable
Make sure you do it a little bit at a time though, esp. the voltage. Its not good to overvolt a CPU.
Obvs. Keep your eye on temps, you dont want to go above 62c with this chip, also with that cooler and mboard see if you can hit 4.7/4.8Ghz, good luck!