I took at peek over at robucket.com they use the following for their single post 4040 build
3/4hp 110v electric motor (can be wired for 240v)
190gph procon stainless pump (with adjustable internal bypass)
I don't know if that is 'just enough' to make it work or there is some wiggle room on psi and hp to make the membrane function efficiently. I went with a 330gph pump for two membranes and a 1hp motor and it worked well, I did a lot of shopping to find a motor that was in my price range that was the right RPM for the pump and had to HP to push it. I originally had a 1/2hp pump with a 125gph procon, it has two 2.5" x 40 membranes, that was a factory machine that functioned fine at 200 psi. Again, not a specialist, just observations on what works, and what others are using.
2023 - 38 Gallons - RO broke, Buckets didn't run, rebuilt vacuum pump mid-season, still made good syrup!
2022 - 52 Gallons - DIY RO, 50% less fuel, no late nights in the shack!
2021 - 48 Gallons - new pans, new arch, lots of new taps and tubing
2020 - 32 Gallons
2019 - 27 Gallons