Thank you for the recommendation on the filter size. I believe I've got that nailed.

60 sqft DE with a 1 hp two-speed pump on a pool/spa with a total capacity of around 12,000 gallons.

There have been questions posted on here asking if it's possible to make your filter too big. Well, one consideration is to make sure that the pump is big enough to provide the required backwash flowrate.

I had some nut from Pentair trying to tell me that, because a 1 hp pump would deliver only 70 gpm at 65 feet of head, it wouldn't be large enough to meet the backwash requirement of 1.5 gpm/sqft (90 gpm).

I could feel my blood pressure rising as I tried to explain to him that, during backwash, the system resistance wouldn't be nearly that high.