As according to my review in order to overclock under a stock heatsink u might wanna consider to remove the IHS... but u gotta do it carefully though, try to visit my website www.xpentor.com find an article about removing it. it's well worth it. 6C difference!

Be careful when increasing chipset voltage by 0.2v or more, make sure you have replaced the current stock HSF to a much better quality one, otherwise you will shorten the life of your mobo , the day when once u restarted the pc, it will never boot forever.
Swiftech and coolermaster blue ice are the good ones that i have used. Look for it.