Thank you Mark! Glad to hear I don't have to worry. The DE6020's manual shows a "design flow rate" of 120gpm. I guess that corresponds to your second number?

I have 4 jets in the spa and the piping feeding them out of the equipment pad is 2" but not sure it stays that way underground. I don't know the size of the spa jets unfortunately.

I filled up the PF Pool Chart. I so far run the VSP for 21h15 a day at 600rpm and at 2400rpm for 2h30 when my Polaris 380 is running its 2h daily cleaning powered by its PB4-60 booster. Since I have the booster pump, could I reduce the VSP speed to the 1000rpm (or less?) at which I often see the Ecostar being recommended to run for max efficiency? How do I know I am getting proper skimming other than seeing all debris not making it in the Polaris ending up in the 2 pool skimmers (spa has none but overflows in pool)?

When I run the VSP at full speed there is no air in its basket (there is air however at much lower speeds, is this normal?), I hear some noises (sounds like small stones) around the 6-position variflow valve interfacing the filter: the equipment installers said this is normal due to the high water flow. I do hope that is nothing bad like cavitation. For information, I made sure more than 10" of straight piping feeds the VSP.

I am reading the "BBB" to get up to speed re testing and what I am learning is very interesting and quite exciting :-) Once this is understood and used, I will look into remotely controlling the system for spa operation...