TweakTown uses a different method for testing CPU heatsinks which allows for an even playing field across all product tests. We feel that by using the same ambient temperature and strict lab-like testing procedures we are able to accurately compare one product to another. More information on our testing procedure can be found in the T.E.C.C. article here.
One of the best things about water cooling is that your system processor temperatures do not fluctuate a great deal between idle and load. This becomes important when overclocking because you want a solid temperature so that your system doesn't crash when it is being pushed harder.
The Thermaltake ProWater 850i does a really good job of keeping the idle and load temperatures very close together, giving you a solid foundation for achieving a stable overclocked processor. The single 120mm radiator unit is holding the system back a little; a dual 120mm radiator would be able to hold the temperature a little lower and a little more stable.
The fan with the ProWater 850i is user adjustable and uses a 4-pin Molex connector, so you will not be able to take advantage on your motherboards built in 3-pin power circuitry that would raise and lower the fan speed as needed when the processor temperature reaches a set point. Since we test the cooling fans at their full 12-volts under load and 7-volts at idle, the test takes the user adjustability out of the equation for the sake of achieving the most accurate Thermal Test. In real world practice the users can set the fans to their liking, which all but eliminates the SPL test, other than the best thermal performance settings.
When the Thermaltake PW 850i is set to just above audible levels, the entire cooling system is very quiet in relation to other CPU coolers we have tested. Thermal performance is lowered a small amount, around 4 degrees Celsius at load.
The coolant pump on the PW 850i can be the loudest part of the cooling system if left sitting on the bottom of the case. The pump has a vibration and will resinate through the entire case, amplifying the external sound you hear. To eliminate this, take an old or new foam mouse pad and cut it to make a base for the pump system to rest on.