well like RTon20s has said, DO NOT, and i repeat DO NOT RUN HALF OF YOUR 4 LINK TO THE REAR! learned from my mistake. originally we built a canti 4 link for mine where i got +15" of lift out of the rear. the severe pinion rotation made my truck only drive-able for the lower half of the lift. locked up i could idle/cruise along at about 5 mph, but that was it. If and when you run all four bars to the front make sure that you have the same gap between the mounting positions of the 4 link on your axel, as you do as it's mounted on the frame. Both sets of hangers need the same amount of gap from top to bottom to insure the articulation of the axel matches the agle coming out of the tranny. if you have a two piece drive line like me, then you will go through carrier barings, and at 50 bux a pop, after awhile it gets old.
as to putting bags over the axel. i look at it like this, if 200 psi is locked up for your rear setup, and your only getting 6" of lift out of an over the axel setup, from 150 psi on it's gonna ride stiff and bust your kidneys. so you have to figure from about 60-80 psi (ride height) your truck is riding smoother, it takes the bumps a little easier. reason being, it has flex in the bag, the air has space to flex the rubber out and obsorb the bumps in the road. so you have to figure the first 3" of lift ride nice on an over the axel setup. Well, setup on a cantilever(bag on the link), it's multiplying the work load and the lift of the bag. there fore the range of the ride heighth 0-80 psi is doubled now, and it has slop in it to obsorb the bumps. Everyones setup is different, and we all have our "sweet spot" where it rides just the way we want it to, but the bags being over the axel shouldn't have anything to do w/ ride (in my opinion), it just has a smaller range of the "sweet spot". RTon20s is right tho, the sleve bags on a 1:1 ratio, does ride well in the rear, but i think that's because of the slack in the bag, obsorbing the bumps in the road. Now mind you, all of this is also dependant on all 4 shocks being good, and the bag setup being good, the link that the bags are mounted on should be rigid to reduce vibration in the ride. bag setups are only as good as the person installing them