1/2 inch will be fine in your garage. My garage is 24x40 and i ran 1/2 k copper and have no problems. You can flow 375 CFM through a 1/2 orfice and im guessing your running maybe 18 cfm at 90 PSI with your Quincy. If you look at the Milton type M quick connects with a 3/8 fpt the opening in them is only maybe 3/16. I dont think you would see a noticable difference if you went with 3/4 pipe. Just my 2 bits worth of information.