17-20 cfm is very comfortable for a single pro user or serious home use. Motors have also gotten more efficient over the years, on top of the misleading HP numbers. My 5 hp 213 frame baldor motor is 28.5 amps nameplate and the new ones are 23 or 24 amps. The new baldor 7.5hp motors use the same power as my old 5hp. You will want at least a real 5hp compressor, which is 22+ amps and 17 cfm at 175psi.
My pump is rated 17.3 cfm at 175 psi. It might be a hair faster than the 800 rpm that rating is for. When I calculated cfm based on tank fill times, I got 20 cfm. 2 stage is better because of the higher pressure. If you get a single stage the might shut off at 125psi, it won't start until 95 psi. If your tool needs 90 (while the air is flowing, vs. measured with the tool stopped) it doesn't leave any extra pressure. Hoses, regulators, filters, fittings, etc. will reduce pressure and flow.
My blast cabinet has a scatblast 20-25 cfm gun and tip. With 3/8" hoses, high flow fitting, etc. it keeps my compressor running constantly. They have tips as small as 10 cfm, but blasting is much slower. Running a die grinder on my compressor is great as it keeps up fine. The cnc plasma table works great, but hypertherm says it takes about 7 cfm and it cycles the compressor every 3-6 minutes on an 80 gallon tank and the switch is set to shut off at 170 psi and on at 135 psi. This keeps the pressure above 100 psi after the hoses and filters.
Anything less than a real 5hp 17 cfm is going to be a waiting game or slow work with smaller tools or restricted hoses. I would love to have a 7.5hp setup or larger, but it isn't really needed since I do this stuff part time in my home shop. The most demanding use of my compressor is blasting for a couple hours or plasma cutting for a few hours. With the modifications to my blast cabinet and the right media, it goes quickly, but I am usually doing small parts or prepping fabricated parts for powder coating.