We use almost exclusively Pentair Intelliflo pumps, but for much more reasons then efficiency, and some that might even out way the efficiency. the most important factor of the Pentair Pump is that it is a (PMSM) Permanent Magnet Sychronous Motor.  If you want to know what that means technically, check out this blog (http://www.poolgeniusnetwork.com/profiles/blogs/motor-efficiency?xg_source=activity)  But the jist of it is that the Pentair Inteliflo pump is 30% more efficient than other pool pumps either 1 speed, 2 speed or multi speed.  For any given output the pentair pump is 30% more efficient - period. They are also because of the design much more quiet. In addition to being more efficient for any given run speed,  they can be "tuned in" to exactly what pump output you need so no energy is wasted. Equate this to driving your car, you would not control the speed of a car by putting the accelerator on the floor and then riding the brakes to control the speed, but almost every pool/water feature is controlled this way by valving to control flow. One pump can also do a multitude of jobs by valving and adjusting speeds. Any fluid system is also more efficient the slower the velocity of the water (almost exponentially decreasing friction), so you are able to get enough turn over rate at a snails pace by running the pump 24hrs a day while costing you much less money. Lastly maybe the most overlooked advantage to a VS pump is the ramp up and down in speed when turned off and on. Turning off and on plumbing systems with a lot of water in transit (especially when the typical pool is designed improperly and velocities are high) causes a tremendous impact to the entire system. Everyone has seen the pump basket that shoots water out of it when a pump is turned off. In larger commercial systems with 6-8-10" plumbing, I have seen filters the size of a volkswagon jump off the floor upon start up or shut down from the impact. An inteliflow or Acudrive equipped commercial system ramps up in speed and down in speed eliminating all the impact. Equate that back to a car, you would not slam the accelerator to the floor for take off (at least not all the time) or slam the brakes and skid into a stop, to do so would wear out the brakes, tires, and engine, and be less efficient. Same holds true to pumping systems. If you are not already a believer in Pentair's Inteliflo pumping systems, you better catch up. Also make sure to do your research, not all advertised Variable Speed pumps are PMSM design, nor do they have infinite speed choices.