Different people mean different things by marginal electrical savings, and here on the gulf coast our electrical rates are relativley low compared to some parts of the country. Still depending on the size of the 2 speed pump you can probably save a couple of hundred dollars per year by running it twice as many hours on low instead of on high (moving the same amount of water). As 2 speed pumps tend to move about half as much water on low while drawing 1/4 the amount of power. The other thing most people do that wastes power is they run their pool pump / filters for too many hours per day, the only real way to know how much you should run your filter is through experimentation, keep shortening the run cycle until you start developing water clarity issues, then turn it back up a bit. The X hours per day are just ball park guidelines, and it is a BIG ballpark. Many members here have found they can successfully filter their pool with only 4 or 5 hours of filter run time on low speed, after spending years following industry standard one size fits all suggestion of 10-12 hours of filter run time per day.
Ike