19 December 2018
Hello James - For your situation, my first choice would be the Pureline Prime 1.65 VS (PL2605). The Prime's water curve is similar to the WhisperFlo but with the variable speed, you have the flexibility of running the motor from 600 to 3450 RPMs. This means you can flip between max savings or maximum pumping power depending on your need.
Your other option is Pentair's Inelliflo VS (011018), which uses the exact same housing as your Whisperflo. There should be little replumbing if you go this route. But the downsides are they the IntelliFlo is almost double the price and the motor is a 3HP. Because your current pump is only a 3/4 HP full rated, you may not be able to use the full capability of the pump. Check your filter for allowable flowrates, or the model number of the filter.