Awhile back I emailed Pentair asking why they didn't use the energy efficient version motor for their two speed pump. I just got the response, saying they consider the 2 speed energy efficient because of the lower speed (duh) but if I wanted a motor with less amperage to look at the WFDS-4 1 hp 2 speed. So I did.
This is a comparison between the two 2 speed, full rated options-
Spec 1 hp 3/4 hp
SF 1.65 1.63
Full speed amps 7.8 14.6
Low speed amps 3 4.7
Looking at the flow chart, the 1 hp has about 15-20 more GPM than the 3/4 hp at any given head. I know the higher flow will increase head, but unless I'm missing something (likely), even if the head loss and flow was identical it appears the 1 hp would use less energy, and since it isn't likely that head loss would be identical it would use less energy AND provide higher flow, allowing for shorter run times and even more savings.
Seems like a no brainer, but perhaps that's what I'm being?