Advice needed to select an energy efficient replacement motor

My motor is screaming at me and I'm planning on replacing it with the most energy efficient option that still functions well. The pump I have currently is single speed (details below). Here are my pool specs:

18,000 gal, AG steel wall/vinyl liner. One drain, one skimmer. Installed in 2008.
Filter - Pentair FNS Plus Vertical Grid D.E.
Pump - Pentair SuperFlo 3/4 HP, 230V self priming, single speed
Aqua Rite Electronic Chlorine Generator, Turbo Cell
Dolphin dynamic cleaning robot, auto cover, no water features

What would you guys recommend I replace this motor with? Do I need to stick with single speed because of the DE filter? Or, can I get away with a variable or 2 speed pump? Thanks in advance! -Ryan