Law of physics on the water pump issue. Stock pump moves "x" amount of water using "a" horspower. High flow pump move "x+y"water using "a+b" horsepower at the same rpm. Reduce the rpm by the appropiate ratio on the high flow pump and you will come back to the same flow as on your stock unit. Since the movement of water is "work" ie engery consumed, it will take the same horsepower to move the same amount of water. Nothing really gained. Money not spent wisely. If it's HP you want, go underdrive with a stock pump. If cooling is an issue go overdrive with high flow. One more thought. The 1-5 HP gain might give 3 at the wheels. What does that translate to in ET.
Wish these were my original ideas. They are not. If you want are more detailed theory, try this web site
http://www.stewartcomponents.com/
They are much more articulate.
I need cooling, My Stewart Water Pump is on the way.