Well, my compressor is overkill for painting. I went for the Sears Craftsman 80gal@175psi 2 stage 5.4HP because I wanted something that could do sandblasting work but keep the price under a grand. Got it for $995 on sale with 0% financing on the Sears Credit card. Heavy sucker @450lbs and a b@tch to get into the basement where I run it.
For painting I fill it up with air then turn it off. The regulator (sold separately) gets set about 25-35 PSI. The big gun uses maybe 1/2 of the 80 gallon tank between paint refills, the small gun barely puts a dent in it.
It is awfully handy for running sanders, grinders, needle scalers, etc tho. My wife uses it to dust off her fake plants and furniture and says its the "best thing I've ever bought...."