The variable speed pump are more efficient for two reasons:

1) You have the option to run them at a lower speed for a longer period of time. This results in much lower losses due to resistance within the pipes and filter. As a result, less energy is used per gallon pumped. I don’t think it will effect heating time but it will need to run longer for the same water turnover. If you need the high flow for a spa or pool cleaner, plan on another $500 or so for an electronic controller to change the speeds for different modes.

2) This pump probably uses a three phase motor with an electronic motor controller. I think these may use 10% less energy per gallon pumped. If you are currently spending $30 monthly on pool power, you can reduce it by $3/month.

Mine is a Pentair Intelliflo. The motor controller went bad after 3 years (out of warranty). Replacement cost for just the controller (no service guy or installation): ~$900. The controller is fully potted in epoxy and not repairable. I wouldn’t install another one….

If you don’t need a high speed pump for a pool sweep or spa, you might consider just buying a smaller pump to reduce friction losses and run it longer.

I suspect the payback period is nearly forever. On the plus side you will feel really green.