Yea, i'm runnin a single six right now, and if i'm already up, with a full tank, i can play for a second, but if i'm at 120 or so, i can't really do much.
The pressure the bag runs at is totally dependent on SOOOOO many things.... tire/wheel size, front cup size, rear setup in how the bags are placed, if you have shocks or not, how much the truck weighs, how much the driver weighs, the type of bag used.
Your bags will probably never see more than 125 PSI, because the front and more than likely rear suspension will fully lock before that. As far as volume... if you really wanna know... fill a bag up with water, then empty it into some sort of measuring device, and calculate what the cubic inches is from how many ounces of water come out.