Single vs two stage compressors have no effect on this. If you have 90 psi in the tank, you have 90 psi in the tank.
There has to be enough
extra pressure in the tank to allow pressure loss in the hoses/plumbing between the tank and the tool.
90 psi in the tank gets you 60--70 psi at the tool when the tool is working, but the tool generally* needs 90 psi to achieve rated power. (*Aircat, for example, goes against Industry Standards, they inflate the power of their impact wrenches by promoting use at 125 psi instead of 90 psi.)
The usual single-stage compressor is limited to 120 psi. Some newer single-stage compressors go to 155, and that's probably sufficient. But 120 in the tank may or may not get you 90 at the tool, with the tool running/working. AND 120 in the tank drains down to whatever the compressor pressure switch engages the compressor again--and by then the tool is starving for pressure and volume. Smaller tanks make this worse, as tank pressure bleeds-off faster.
The practical result is that MOST (not all) single-stage compressors result in low tool power compared to the rated power of the tool, due to lack of usable air. Installing a temporary pressure gauge at the tool end of the air hose can be eye-opening.
I started in '97 with a 110-volt, 20-gallon compressor. Tried to air-chisel the rivets on upper ball joints. The air hammer would run for about three seconds before pressure was so low the air hammer was useless. That compressor didn't hang around long, but that's another story.
Moved up to a "220-volt, 5-horse, 60-gallon single-stage" compressor. When porting cylinder heads or other die-grinder work, the pump never shut off and I had a miserable time with water in the air lines. Intermittent use--impact wrenches, air ratchets, etc. worked pretty good, but I never used a pressure regulator. I never needed less than "all the pressure I could get."
For nearly 20 years, I've had a "220-volt, 5-horse 80-gallon two-stage" intercooled and aftercooled compressor; I never have water in the air lines, and I can run any single tool I own continually and the compressor shuts off now 'n' then for cooling. The compressor pressure switch is set to come on ABOVE the regulated pressure, so the air tool gets a steady supply of air. The metal plumbing near the compressor has a "Y", one branch is regulated, one branch isn't. I can theoretically run my air tools off of 180-150 psi if I had a "tough job"; but so far I haven't needed to connect to the unregulated branch.
Yes, the Prevost couplers are expensive. Try
one at the tool end of your air hose--the one that gets connected and disconnected the most. For me, the big deal is the ease of connecting while under pressure. The Milton V "high flow" couplers are nasty for that; Milton T (Tru-Flate "Automotive Interchange" style) or M ("Industrial Interchange") are not
as bad, but not as nice as the Prevost.