I have a Corsair H100 with 4 AP15s cooling my 2600k at the moment. It works pretty well to be honest, and I have been pretty happy with it. The only problem was that I had to mount it in the bottom radiator bay of my CM690-II case as there wasn't enough clearance on the motherboard heatsinks in the top bay - even with two of the fans mounted in the roof section. Everything is fine while the system is running, and the pump can circulate the water well. The problem occurs when the system has been switched off for a period of time. An air pocket seems to form in the pump and therefore no water is circulated! I have to move the case around to get the water to get into the pump before it starts to cool the system - I am guessing this is because the radiator is designed to be fitted above the pump. Looks like I will be sending it back and getting a proper loop after all, unless someone can come up with another suggestion?