My Cooling Improvement Project (hopefully)

Charrlie_S explanation makes sense. If the water pump cavitates, you will have less water flow rate, which would decrease heat transfer in the block and radiator. One would need more instrumentation, like flowmeters in the plumbing to know what is really going on. If restrictors work, by all means use them. I doubt that water flow would channel differently in the radiator at higher flows. For that to happen, the water would have to enter in a narrow, high-velocity jet. You would need a pump from a fire engine to do that in a 1.5"D hose.

AC theory is less abstract than Dorian's explanation. It cools by boiling off the refrigerant, the same as how any can pressurized with liquid (hair spray, propane) cools as you use it. Since we don't want to keep throwing refrigerant away, we condense it outside (re-compress & reject heat) and re-use in a closed cycle.