CPU: Intel i5-2500K
Thermal Paste: Noctua NT-H1
Motherboard: ASUS P67 Sabertooth
RAM: 2x4GB Patriot Viper Xtreme II 1600MHz DDR3
OS HDD: Patriot Pyro 60GB SSD
Secondary HDD: Patriot Wildfire 120GB SSD
OS: Windows 7 Professional 64-bit
For our load tests, we used Prime95 to stress the CPU to 100% and then used RealTemp to record the temperatures. We treated the Kuhler H2O 920 a little differently since it takes the water temperature a little while to come to equilibrium, so we let the test run for an hour before recording the temperatures to make sure the "cold start" temperature didn't provide an unfair advantage, since we allow our air coolers to warm up before recording the temperatures. We tested two different conditions of the i5-2500K, the first is completely stock and default settings, and the second is overclocked to 3.8GHz and 1.26V. The single value recorded is the average temperature of the four cores.
Overall, the Kuhler H2O 920 does quite well, and there's a bit of encouraging information in here as well with one of our biggest gripes with the cooler. Using the "silent" preset, the fans are pleasantly quiet, and although not an ultra-quiet setup, are nearly indistiguishable outside of a closed case over the other fans. We allowed the fans to ramp a bit until it was on par with what we would hear out of most other coolers, and that's the "normal" test we used. A light hum was detectable, but not much past that. However, when the fans are amped up 100%, they're only tolerable with a good set of noise isolating/cancelling headphones with some volume blasting into them. They're far too loud for 99.9% of us to use. With that said, the encouraging part is that the "normal" setting didn't trail by much, at only 2°C under full load when overclocked.
The Kuhler H2O 920 comes close to matching the Cooler Master TPC-812, and matches it at full speed, which is one of the better air coolers we've tested. We also expect the Kuhler H2O 920 to also have a greater heat dissipation capacity, which means you can transfer more heat into the system before it begins to heat up. This is largely due to the advantage of using water cooling: water itself can store a large amount of heat. Ontop of that, the ability to pump water through an intricate network in the radiator means you get overall better transfer to the heatsink.
Another note is that the cooling is more uniform with the Kuhler H2O 920. What I mean, is that when we monitor the temperatures, the individual core temperatures are very consistent. For instance, we'd see load temperatures like, 46-48-48-48. With air coolers, the heatpipes creat hot and cool spots across the chip, and we'd see something more along the lines of 45-48-51-44. This can pay dividends when pushing your chip to the brink, as the individual temps will be more uniform, but for the most part is more of a sidenote than anything.