Airbags provide up to 5,000lbs of leveling and should be plenty, especially with upper stableloads.
Personally I think the lower stableloads are bad for springs, they induce a unnatural pivot point which can stress a spring in a manner it wasn't intended for.
I would skip the Rancho's, of all the shocks on all the vehicles I have ran I have never been as unimpressed as with the 9000's (used them on 3 rigs of various size and weight). Bilstien 5100's are night and day better than Rancho's 9000's, and I didn't know what a good shock was until I ran them.