You might be better off with a larger compressor if you were spraying cars, or a conveyer line of production guitars, but a single guitar doesn’t take much spraying at all before you’re finished. The motor run time cycle is important, and most compressor motors are rated for a 50% duty cycle (50% on, 50% off). More than 50% and the motor can burn out. But you’ll probably have the compressor run once for a couple of minutes when spraying, and then you’ve finished and it’s probably 30 mins or more before the next coat goes on. So your worst load cycle is probably no more than 10% and generally less.