This is a more complex issue then just flow or cavitation. Misapplication of principles. What does radiator flow mean? Water flow or air flow? Flow alone does not control heat transfer rate. Surface area, material, Temp difference of air and water, design all factor in for radiator heat transfer coefficient to maximize the cooling of the water at the radiator. Contact time in both the radiator and the engine do matter. Cavitation is not only the material damage to the impeller, it changes the efficiency of the pump and you lose flow volume. Capacity of the system matter too, with regard to equilibrium of the system.

Time matters. Take a frozen radiator, and 200 degree water and push it through the radiator in 1sec. What is outlet temp of water. How about after 5 sec, one minute? Same with the block.

If the radiator was cooling incoming 210 degree water and dropping it to 150 at outlet what would happen as the water temp in the engine started to drop to 175. The thermostat would close and reduce the flow to help keep the motor water temp at the optimum temp so the block would be at the correct temp for combustion and operating design. At that point, what good would this high capacity radiator, fan, and water pump do if the system is causing the thermostat to cycle closed trying to keep the the motor at the correct operating temperature. North Dakota in the winter with no thermostat. What would max engine temp be under those conditions.

Look at service manual, race manual, and the Chrysler training material, and everything was a trade off. The hemi and the small impeller was a performance move to save HP loss. Same with the centrifical fan for hemi versus thermostatic one for AC cars. I think Superbirds where having cooling issues and the recommendation was to go to a fixed fan blade. This would be a HP loss at high speed though. Look at all the combinations of fan types, blade lengths and pitch, impeller types and your head will spin.

If you are have a cooling issue, I would look at the block and head cleanliness and your radiator. A good cleaning flush. You can use a temp sensor gun to see if you have hot spot on the engine, head, manifold causing excess heat generation. A good solid fan will maximize air flow at idle. I think the pump impeller would be the last thing I would look at unless some thing wrong internally with the housing and the water is not flowing properly.

That test the RV guys did was interesting reading as it was hard to come to solid conclusions on what is best for cooling if I remember right. Which impeller do you want to use? Notice the orientation and size difference, and this doesn't even include the turbine style plastic and cast blades used in the mid 60s.