Just to add to this....the fact that the thermostat controls coolant temperature by controlling coolant flow indicates that whenever there is sufficient airflow through a properly sized radiator, there is excess flow capacity available; otherwise, the thremostat could not manage temperature by opening further and allowing more flow. The only time that this is not adequate is when there is low airflow through the radiator; that is the one case where higher pressures to force more flow will be of use. But, as Del points out, a lot of that is dependent on impeller clearances.
And yes, a water pump is not a posittive displacement pump like an oil pump or Rootes type supercharger.
