Water cooling has the advantage of lower noise and more efficient operation at high overclocks/volts with reasonable temps. But, it is still limited by the Delta-Temp with the reference being ambient temperature. As with most radiator setups, the higher the Delta-Temp, the more efficient it becomes up to the practical limits... but that is too high for CPU's normally. All the water really does is substitute for copper as a heat transport medium... but it allows us to adjust the radiator (cooler) characteristics several ways. Bigger Rads, higher power fans, larger tubing, more flow... etc...
In the end, it's all about displacing heat from one location to another. A triple-120 (360) rad can handle 350 Watts total with 65 CFM fans but needs 135 CFM fans to handle 600 watts (or more) and keep temps in limits. My 800D box is setup to be able to switch from 7v to 12v fan power for overclocking the Sabertooth mobo and two GPU's... but handles things fine at stock speeds/clocks at 7v using 135 CFM fans. Soo, when I want it to go fast, it also gets VERY noisy like the inside of a data center... LOL!
All depends on what you want and what you can tolerate... I've learned a lot in the last 1.5 years overclocking and water cooling and decided a 1/3 increase in electricity used is not worth the 15% CPU/ 30% GPU overclocks on that 800D box except for BGB... Sooo, I tend to run things more or less stock speeds now since the payback for an overclock is less than just adding another box.
Another for instance is it takes about a 40% power increase to get a 25% overclock on my main system... it's worth it there sometimes because I use the box for many things... but the other boxes.... well, just add another PSU/CPU/Mobo to the mix and it pays for itself in power vs. points within 6 months or less.
