I've had 40 psi at the tap for the last year. HF5 membrane. I don't use a booster pump and my 4040 r/o produced about 2 litres pure to 2 litres waste in the winter. TDS at the tap = 125 and TDS after r/o and before DI = 2. Our water volume isn't brilliant as we are on the end on the ring main.
I'm happy with that.
My advise would be to run it for a while and keep an eye on performance - you can then make an informed decision later.