There are two big advantages to 2-spd pumps.

1) They are INCREDIBLY quiet at low speed.

2) It will take 50% to 100% longer to turn over your water at low speed, but will burn 1/3 the electricity doing so.

A third advantage I have noticed is that my sand filter, even though it's sized correctly for full speed, STILL cleans the water better at low speed. I guess there's more time and less water pressure allowing the sand to catch more.

Sorry, but I can't do the feet of head calculations--others are better equipped to do that. Couldn't get your link to work, either. Hayward SuperPump is only one brand and model. There are others just as good, maybe even better, but I've been very happy with mine.