As darran has said, psi is pretty much irrelevant over 3000 psi, but LPM is massively important for cleaning power.
I got terry from jetmac to sort me a 23lpm machine, by using a belt with less teeth than running the pump at 21lpm. I’ve also got a 20 inch FSC from him, it’s a great bit of kit.
I’ve had a few machines over the years, usually 21lpm but the extra 2lpm works wonders for an FSC. They are pretty useless for deep cleans and getting moss out of block paving though. That’s where the turbo nozzle is needed.
Find out what LPM your machine is, then think about which jets will work in an FSC based on your machine 👍🏼