I can speak from experience...

My old 1.5 hp pump sprung a leak so I replaced it with a 1 hp single speed Whisperflow pump. At that time I had a hayward sand filter rated at 62 gpm (3.xx sqft). The 1 hp Whisperflow easily outperformed my old 1.5 hp pump but it was to much for my sand filter. After a backwash the pressure would start at 22-25 psi. Also I would get a little sand in the pool so I replaced the sand and checked the laterals, everything was ok. My only guess is the 1 hp Whisperflow flowed to much for my little 62 gpm sand filter and that it was pushing sand through the laterals.

This year I had the opportunity to replace the sand filter with a DE filter. Hindsight being 20/20 the sand filter was definately undersized for my 2" piping and 1 hp Whisperflow. The DE filter runs at 10-11 psi compared to the 22-35 psi the sand filter ran at. The only thing that changed was the filter!

If I had it to do all over again the only thing I would change would be a 2 speed 1 hp whisperflow!

For now you could buy the 2 speed 1 hp and just use the low speed (with your sand filter).