Im not to happy about it. Although this suggests otherwise
http://delphi.com/pdf/techpapers/2000-01-0579.pdf
SD = Q/dt = W/C
dt = water in temp - air in temp
Its applied to car heat cores so its applicable to water cooling. In summary coolant base line temps (in let conditions) are only a small effect but flow rate is very important.
Would do more analysis but have job applications to do.
EDIT: Should note that rads dont have 60kph air inputs and such high flow rates.