CFM is the thing...
John,
It's best to go by CFM (cubic feet per minute), not HP. Not all pumps that require a 5HP motor are the same. Check the output at 90 PSI, which is where I run my drills and die grinders.
I have been using a 2 cyl 5HP wet pump compressor with 25 gallon tank, rated at 6.4CFM @90 PSI. It is fine for riveting and most drilling. While drilling wing skins I was operating that drill continuously, and eventually the RPM would slow, and the compressor ran most of the time. This was not a problem, as the pump is cast iron and is built for it, but I don't like slowing down to wait for the compressor to catch up.
What makes the compressor run is how many CFM your tools draw. Cheap drills will suck tons of air, as do blow guns, conventional spray guns, DA sanders, bead blasters and die grinders. Is my 6CFM enough? OK for riveting, and adequate for drilling if you don't mind waiting. But, When dressing parts with a die grinder and scotch brite disks, 6CFM was not enough, the grinder would lose RPM, and I'd have to wait for the compressor to fill the tank. the Pump also got pretty hot.
Also, I've been spraying furniture with Lacquer in a cheap automotive paint gun, and here too, during a long session, I'd have to stop painting to wait for the compressor to catch up. In hindsight, I wish I had spent a tad more and gone with one that would put out above 12 CFM at 90 PSI, which is what most of my sanding and grinding tools need.
I'm now building a new shop and upgrading my compressor to a vertical tank model, that'll do 14CFM at 110 PSI. I got tired of the compressor running all the time, and I'd like to run a bead blaster. This will be the last compressor I have to buy, cause it'll run anything I hook up to it. Northern Tool has many good compressors on sale with free shipping right now.
Another tip, If you can put your compressor in another room, or mount it outside, that would help to lessen the noise.
Art in Asheville
RV-8 finishing