We use 15 GPM Air pumps, but we clean several roofs a day, and traffic here in Tampa can be really bad.
Thus, speed is of the essence.
Most of my roof cleaning local friends use the Delevans wih 1/2 or 5/8 hose, depending on how much space they have on their trailers for the appropriate hose reels.
It took us over 15 years to build up a roof cleaning business to what it is today.
Now, it's mostly gravy, just re writing past customers.