Getting to 4.0GHz should not be too difficult or produce too much heat. Any decent 120mm tower-style cooler should be sufficient. I use and recommend the Xigmatek Gaia over the more frequently parroted but inferior Hyper212 EVO:
http://www.techreaction.net/2011/07/07/review-xigmatek-gaia-sd1283/7/
http://www.techreaction.net/2011/11/27/review-cooler-master-hyper-212-plus/4/
Unlike the Hyper212 EVO (ignore the URL; it IS the EVO they tested), the Gaia never throttled, although it wasn't always the coolest depending on the fan used. Both got awards, but if you factor in the price, the Gaia wins hands down.