Not an expert on this by any means, but I have been told, sometimes those HV pumps have a reverse effect. They pump coolant so fast, it is not in the radiator long enough to cool. As I said though, I'm no expert.
From what I've read they really don't pump that much more if any. I think the thermostat or spacer will really keep it from flowing so fast as to not have enough time in the radiator or in the motor to transfer the Heat.
