So you are saying that you are not slowing the pump down to save energy, you are adding a high speed you don't usually use? That is a whole 'nuther thing.
Pools are usually designed to turn the water over x times a day and in a residential pool they just turn the pump off when that is done with a timer. I am still not sure how a multi speed motor running at a fraction of full speed uses less energy that a pump that is turned off.
Since a commercial pool is required to run all the time, they select a pump to get the required turnover number in 24 hours with a little wiggle room for inefficiency gain as it ages.
The real answer should be in the paperwork submitted when the pool was permitted. There should be flow rates based on the suction and pressure readings at the pump. Then you look up the pump specs for the rate.
