Thanks for all the comments. I spoke with the guy at Eaton and he said there is no real formula to determine cfm at different pressures. He just said all compressors will produce more cfm at lower psi. His best guess was that his 14@90 (that's the more accurate free air rating) compressor will pump out 16@40.

About ratings, you guys are right. Lowe's/Home Depot compressor ratings are all BS. They typically advertise horsepower just at start up, which is much higher than running horsepower. And their cfm ratings are not a true 'free air' rating. Which again, just inflates the numbers.

After talking with Eaton, it seems they know what's up. They advertise their systems using 'free air' and 'true horsepower' ratings.

About that comment that a small compressor can run an HVLP gun. What compressor are you using? I have two smaller 30 gall compressors with dinky 1.5 horse motors (not a true horse rating, so it's even less) that I got at Lowe's and they can't keep up at all with my gun. Only a few seconds and then the motor kicks back in. Always behind. Those small ones, at least what I'm using, are worthless. That's why I'm upgrading.