I am going through the same issue. It seems like the Variable Speed Pumps give you a one size fits all and then you tune it to meet your needs. The most popular is the Pentair Interlliflo but it only has a one year warranty. My issue with them is they have a lot of complaints and all they are doing is taking a 3 phase motor and mating it with a VFD. Minimally they should be giving 3 year warranty.