I have the same CPU and case on a MSI P6N Platinum board with no over-clocking at this time. Using an Enxotech Exctreme cooler. Idle is 28-30, under load no greater than 37. I added an additional Noctua 1200 rom case fan in the middle hard drive area. Bottom case fan set on medium, top two case fans on low. Enzotech fan set around 1700rpm. Other options I would consider: Thermalright's which I've used on another setup with excellent results and the Zalman 9500.
I have a E6750 overclocked from 2.66 to 3.4 - with a Scythe Ninja attched, and I use OCZ thermal paste. Works really well and I don't recall it being particularly expensive about £30 I think. It can be run with or without the included 120m fan. It's huge so you need to check you have space but a good buy. Ensure you get the revision 2 version otherwise it can be a pain to fit.
It dropped my CPU idle temp by about 15C pre overclock and post OC at idle it runs at about 22C and only rises to about 32C under load.