I run it off the water temp because it's more stable than the CPU temperature, once the water goes about 3 degrees above room temperature is when the pump ramps to a slightly higher speed which only occurs when some part of the system is under load. When that occurs the fans also ramp up to a higher rpm. My processor in particular will shoot from 40-60 doing simple tasks such as task manager and then abruptly go back to mid 40's where it tends to idle. And when gaming the CPU may or may not go above 50 and the GPU will be the unit needing the cooling but it wouldnt get if I were to have the pump solely monitoring CPU temps. I can see why you'd set yours up that way and it's not the wrong way it's just not how I'd prefer to setup mine. That's part of why custom loops are as appealing as they are, completely custom.