I have 20 year old 8 gallon wheelbarrow compressor with 1.5 HP motor and have never run out of air. It specs Free Air CFM @ 90 PSI - Air Compressor : 7.4 CFM
Jenny #K15A-8P
It does kick off and on, but does keep up. I have used a 20 gal slave tank in the past for other projects, but it has done fine cutting without it. I have an Everlast 80S plasma cutter if that matters.