Are you planning to be looking for max wheel travel while loaded up?
Adding the air to the bags brings them back to near the unloaded rest position, so you potentially have the same travel with a greatly increased spring rate.
Basic static height only changes as much as you want it to.
Personally I like my rear axle to sit 1-1.5" lower loaded than empty, so that's how much air I put in my bags and the ride is great!!! That's the beauty of airbags, they aren't setup for only one load as they are adjustable to each and every load. If you need more than 5,000lbs of lift you are probably overloaded anyhow.
I am not sure my truck has ever been on a frame lift. I know I haven't done it, and I haven't seen anyone do it at any of the shops I have been to.
On my Tacoma the shocks held the axle at full droop, not the bags. I think that's hard on the shocks too, and personally don't like frame lifts for some of those reasons. They are super handy thou!!!
