My 04 GU ute has arb 400kg rear springs, coil rite bags. Just done 9000k trip in rough country with slide on. Fully loaded with water, fuel etc was around 3.9t, know this because put over weigh bridges. Had GVM upgraded.
Handled great. Re the bags I ran 20psi in them all the time, even empty, blew a bag on the Hay river, was caused by a stone getting between the Kevlar cover and the bag, the single bag handled it till I got to Alice and could get another one. Found out not to use the cover on bags as we don't use over 35psi.