Here is some real world feedback from my dually.....i have 6 1/2 valves on mine(4 for front...rear is T'd together)....when the tank is at 200 psi it lifts quick but isnt violent fast....3/8 would be my suggestion....my valves are mounted under cab about middle of rear doors....if you have your front valves mounted at rear of truck it will lift alot slower....i am running firestone 2600s on the front of mine and it lifts my Cummins just fine and rides great teamed up with my Monroe SensaTracs.....on the rear i have a set of Chassis Tech 3800lb bags mounted over axle.....always heard horror stories about CT but decided to give them a try once and im not disappointed with there bags.....and they will handle plenty of weight.....takes about 15psi to ride in the rear and about 100 i can drive anywhere in the front....90 if i wanna ride low....on the rear i have some stock Dodge 2500 shocks off a 2012 truck...my buddy does lift kits for a dealer and he had some brand new ones layin around.....truck rides awesome....i have
people that have never rode in a bagged truck ride in it tell me they cant believe it rides that good....and the more people that are in it the better it rides...hope that helps alittle