If I ran one I would want it to be a brushless permanent magnet motor. This means the pump will have to come with an inverter box as well. I have not seen any of these out there yet.

About the water flowing too fast. I have yet to see any test results or analyses on it but I would note the following facts.

1) Say one pump is flowing twice as fast as the other. The total time in the radiator is the same, it is just there twice as often for the 2x pump.
2) Water abosrbs and transfers heat via convection and faster fluid means higher convection coefficients.
3) At the extremes it would seem faster is better. Why? Well if you have no flow you know what happens.

There is likely an optimum, however, if you have a restriction like a thermostat (and you certainly should on the street) IMO you will be hard pressed to get the flow up too fast.

Kitz