Largest compressor I have used was a 900 cfm. IMO its all about the cfm vs the pressure. I had several townhome systems and one small private homeowner golfcourse.
The largest mainlines were 3" and one townhome had 2 water sources and 3 clocks w/16zones each. What I was worried about was melting down the pvc after the rpz. Systems that large I remove all backflow devices, plus they usally are stored off site. 1 so they dont freeze and 2nd as an insurance policy to get paid.
It felt like all I did was make sure pressure was in check vs discharge air temp and pushing water in the correct directions since there were no isolation valves within the townhome systems.
When I rented the machine the first year I thought I was going to have these systems done in and hour or 2. NOPE The second year brought an employee along and the golf cart and only saved about 40 min. on the large townhome system
The large compressor was a sullair rented from the local cat dealer. The tech told me not to run it under 100psi as it needed back pressure to keep the aftercoller working properly. Well the golf course worked fine at 100psi since I installed the system with a larger compressor in mind.
I wasnt sure how the townhome systems was installed so took a chance at the pressure, so I dialed it back to 90 psi and stuck an oil pan under the machine. At a lower psi the aftercooler for the compressed air didnt work properly and bled oil. I would rather have oil bled from the machine than broken main lines in the ground.
Most system I do range from 9 zones w/5-6 rotors on them up to 30zones. So I use a 185cfm that I own. Its interesting to learn about how things are done diffrently in other parts of the country as I dont think a roofing compressor would work very efficently for us.