I found a lot of great info here http://www.poolplaza.com/C-Pool-Pumps.html Each pool is different. They explain how to determine turn over rates, total dynamic head, maximum flo rates for the filter and how to read pump curves. Once you find out the particulars on your pool then you look over the pump curves and find out which pump best suits your needs. Too much power and you waste energy and your filter is less effective. Two speed pumps are great because they give you both efficiency and power when you need to backwash and vacuum.

Jennifer