You can run up to 5/8" line on 3/8" ported bags and the speed will increase with each increase in line diameter (3/8-1/2, and 1/2-5/. While the threads may be the same (3/8"), the flow diameter (the diameter in which the air flows), will increase with each step up in airline size (using the right fittings anyway). Check it out at
http://www.airridetalk.com/specifications/ and click on the fittings link on the right hand side.