I have the exact same truck that you have, with both upper and lower stable loads and Rancho 9000's. I added uppers first and they did nothing to raise the back end, but did eliminate some sway. Then I added the lowers and it lifted the back a little over an inch, so now I have about 1 1/2" of squat with no water on board. With full tanks and loaded to go, I'm back to about 2". This is pretty good, but I am interested to see how the bags work out for you because ideally I would like some adjustability.
As far as the stableloads damaging the lower overload, I can't see it happening on our trucks. That spring is incredibly thick and tough. I think the stable loads would get destroyed before the spring. They seem to be made of softer steel. Time will tell. Springs are not that expensive, so it's a cheap fix some day in the future if necessary.
I added Rancho 9000's last. The stock shocks had 46,000 miles on them and it was not ideal. I set the back's at 9 and the fronts at 6 and the ride is much more stable. When road condition cause the load to sway, it now recovers with one move instead of wobbling. Don't know if they will last based on some reports from others, but I'm happy with them now. All the shocks I researched had reports of failure, so it's hard to know if these are more or less reliable than the other choices.
Please let us know how it works out with the air bags.