virtualrain, you contradict yourself.
In the second to the last entry you wanted to speed up the fans when the temperature of the CPU is rising, now in your last entry it seems you don't want to do that - because when the water temperature is rsing (no matter why), the CPU's temperature will too
So why should I especially care about the influence of the room temperature when it also affects the water temperature including the CPU temperature.
Let's say my CPU is idle and has 30°C while the room temperature is 20°C. Well, it's summer (in this example *g*), the sun is coming around the corner and is heating the room up to 25°C. If I don't change the fan settings, theoretical the water temperature should also rise by 5°C. Now it's your turn - tell me why I should
ignore the room temperature?
Next example concerning the control via the core-temperature. I load a very large Photoshop file with hundrets of layers and it takes ~1 minute. Of course, the CPU is at full load while loading and the core temperature is rising pretty fast. With your "logic" I should start the fans now. I have only one simple question: why?!
In that 60 seconds the water temperature hardly rises so there is no need to start/speed up the fans. Even if I would start/speed up the fans it's impossible to ge any real advantage in that short time.
As said before: with a fan-controlling dependent on the core temperature you will get a permanent up and down of the fans while using the water temperature will only start/speed up the fans when it is really necessary.
I don't know what processor and energy sheme you are using but my core temperature never stays the same (expect 100% idle/load) and moves between ~30-45°C - and that pretty fast when I start or load something here and there.