We basically used the stock engine (f4i) setup as a baseline, and took water temps before and after the radiator with no forced convection (no fan) as a worst case scenario. Sized the radiator based on the NTU-effectiveness method from there.
In terms of weight savings, just for fun we chopped our main rubber coolant line and replaced it with about 18in of aluminum tube with small rubber ends. We saved 1/3lb over the rubber alone.