My opinion and experience:
I have a Paramount in floor. You need to run the pump at high speed for an hour or two every day for it to do its job. (Note: In Arizona, they work pretty well, and it's one of the Agree to Disagree things for me here-- I do have to vacuum out "rock dust" about once a week because it's too heavy to gown down the main drain... this is actually desirable for the filter's sake. Someplace with a lot of foliage and organic matter I think would be another story entirely.) Beyond that -- on low speed they still do some good. Before I added the SWCG I ran the pump for a few hours at 900 RPM every day in addition mainly for the skimmer. Now I run at 1500 RPM for 12 hrs, 3000 for 2 hours in the morning. I am going to drop it back two hours this weekend because my SWCG is generating more chlorine than I am losing even at 30%. At 900 RPM the flow switch would occasionally trip. The wattmeter didn't change much, maybe 10%.
But really, run it at 3000-3200 RPM for 2-4 hours a day (if you are a high load I'd do on the high side) and then the rest is pretty much optional for the floor system. You'll want to run at low for the skimmer though. I run 100% to the floor on mine. There is no real reason to use the returns unless you need them for maintenance reasons. (Aeration, mixing of chemicals, etc.)