The question from a thermodynamics POV is maximizing the amount of heat removed from the cooling system by the exchanger. The rate of flow for a given system must be in some bell curve range considering all the parameters in the system. I can't imagine just faster or just slower being automatically better. Imagine a system that doesn't move at all. That overheats obviously. A system that flows at some extreme high rate won't expose the heated coolant to the exchanger for periods long enough dissipate the heat (IOW, what little cooling there is will be quickly reheated). I don't recall the formulas for efficiency of heat dissipation, but there is kind of a lot this question. As for the specific question of how much Guy needs, hell if I know, but if there is some "tribal" knowledge that 10gpm is better than standard 5gpm~, there's probably good reason. Certainly stands to reason that if the after cooler is much larger capacity and the fans blowing more air over them, then likewise, you could push the coolant through faster to be in that bell curve of efficiency. Imagine a bell curve with heat removed on the x axis and flow on the y axis. I imagine heat removed to be low with very low flow and very high flow, and to be high with "just right" flow. Or I might be wrong, but that's how I'm thinking about it.
