I switched from a single-speed to a variable speed about two years ago, and the difference on my power bill was pretty noticeable. The trick is being able to run it on a lower RPM for most of the day instead of blasting full speed all the time. It does take a little trial and error to figure out the optimal setting for your pool size and filter, but once you get it right, it runs quieter and more efficiently. Upfront cost is higher, but mine paid itself off in about a year and a half.