I see what you are getting at. In a normal cooling setup, the heat is transferred to a larger area before being absorbed by the water. I looked it up and water has a thermal conductivity of 0.6, copper is 400. So copper is definitely better at transferring heat than water. But all that is meaningless when you have to use a TIM that has a thermal conductivity 3. http://en.wikipedia.org/wiki/Thermal_conductivity Maybe the ideal solution would be to solder the core directly to the waterblock? I don't know, maybe someone with a background in thermodynamics can pop in here and explain the science behind it.