Honestly, you dont need water cooling to get some pretty good overclocking numbers with most cpu's. My 2500k was pushed to 4.8 with a hyper 212 evo, with temps never going above 75c, with my last build(with a corsair carbide 400r case) Now i have the same cpu in a new build, and have a corsair h60 water cooler. I havent overclocked it nearly as far yet, but from what I've seen so far, the temps arent much, if any better than the evo.
The big advantage to the water cooling is the amount of space it frees up on your board. I can add/remove ram, get to all my fan headers, things of that nature with the water cooler that I couldnt do with the evo. Also, your board isnt having the stress of holding up a big, top heavy heatsink.