I have the same EVGA E760 mobo and an i-7 920 CPU - right now, my OC is 3.51GHz and the idle temps are around 27 degrees C with a V8 heatsink air cooler. This is about 30% OC.
You should be able to attain your desired OC with an air cooler. I wish I had a Megahalem heatsink, but my Corsair dominator RAM chips are tall and there is a clearance issue with Megahalems (the fan).
I am not a fan of water-cooling because water and electronics don't mix. Sooner or later there will be a water leak issue.
Hope this helps
In talking with overshocked (he's wayyyy into overclocking), even in his dry ice runs, DICEing the NB didn't help him get any higher bclck, and that the Classy has a very good heatsink anyways, so even for extreme overclocking, it's fine without one. However, if you're going water on everything else to the point where there is little airflow through your case, I'd recommend putting it under water or just adding a small fan to blow over top of it and the VRMs.