The system cfm is restricted to the size of the opening and fittings. If you open the large clean out on the tank, the cfm that escapes through that opening is huge compared to what goes through a coupler fittings or the nozzle of a blow gun. Air in the system is relative to pressure, storage capacity and the cfm of air the tool uses. The compressor is limited to pressure only and CFM delivered by design. It can only make so much compressed air and is limited by the pressure switches within the limits of the design. CFM is just the measurement of air used. You can't make more air than the compressor can put out pressure wise and you can't deliver any more than the hose and fittings can deliver. Adding a extra tank will increase capacity but not the CFM delivered by the compressor or the cfm exiting the hose through the fittings. If it takes 5 min to fill a 80 gallon compressor to 100 # it should take that same compressor 10 min to fill 2 80 gallon tanks. It will take you twice as long to empty 2 tanks over just 1 but it will take twice as long to fill 2 tanks up as well. And like I said earlier, if the air tool or blast cabinet uses more air (CFM) than the compressor can put out you will eventually run out. Time to crack open a beer and let it catch up.