[dsraven]

kina 2 ways to look at the compressor keeps up. really, for continuos use, if the compressor keeps running but also keeps up to continuous draw then it is saving power because the start up draw is more than the run draw (just me guessing there) and the start up is harder on the motor that continuous use.
anyway, who knows how to figure that out because our shop use is varied from project to project. I would say figure out the biggest draw you would have for air and get a compressor that will keep up. if it is something like sandblasting that you will do a single or possibly a couple of times, maybe you just wanna contract that job out and save the mess, wear and tear and the need for the larger compressor.
if spraying with a hvlp gun it will likely use less air than you think, compared to the old higher pressure siphon guns. for spraying it is also important to size the air lines correctly along with the quick connects so you actually get the flow and pressure you need at the gun without a variance when you stop/start spraying. if you set the gun pressure at 10 psi at the gun when spraying and then when you stop spraying the pressure at the gun goes up, spikes, then that is an indicator that your lines/quick connects are undersized.
will you be running some shop air lines as well? if so, have you thought of using pex water lines? no corrosion, easy connections and they hold the 120 lb pressure.