I use a piston Solo backpack. I just use the Tee Jet fan tip that comes with the sprayer. It works great for me. I have calibrated the sprayers and 2 get 1/2 gallon per 1000 sq ft and the other one gets 3/4 gallon per 1000 sq ft. I have never measured it per seconds.
One thing I use is a constanst pressure valve from Gemplers.com on my backpacks. It will keep pressure from going above a certain psi and it shuts off if the pressure gets below that certain pressure. This eliiminates one variable factor anyway.