Even under a modest OC, you really don't NEED an aftermarket cooler.
The stock cooler does a reasonable job of cooling until you get to higher voltage levels.
However, the small fan needs to spin up to provide more cooling, and it will get noisy.
The cpu chip has a TJMAX temperature of 105c. before it will downclock itsellf or shut off to protect itself.
That said, I recommend instead that you invest $30 or so on a tower type cooler with a slow turning 120mm fan.
Something like the cm hyper212 would be fine. The larger fan will provide more cooling and be quieter.