These things have completely stabilized my system. I have two 4870x2s in crossfire and I was getting temperatures under load of 70-75 degrees Celsius or more with the stock fans and heatsinks, even with the fan speed at 80 percent or more. As a result, applications just quit after awhile. Now, I get an idle temperature on the primary card of 29-30 degrees Celsius (the second card is about 33-34 degrees C at idle), with temperatures under full load (e.g. playing Crysis, Far Cry 2, etc. for an hour or more at a time) of 40-44 degrees Celsius maximum. I have had only one crash (playing Mass Effect) since I installed the blocks a week ago, and I am not sure I would blame the cards for that. The only trouble I noticed was coolant leaked from the little screws near the nozzles on one of the blocks when I first fired up the pump. The leaking quit when I backed off one of the nozzles slightly, and it has been bone dry ever since. I am using a Koolance external unit and 3/8-inch tubing. Other than that little glitch, I have no complaints. Great product!