i'm running the kelderman system that attaches to the rear of the springs. they give a very comfortable ride. but have noticed some side to side movement of the axle, due to the rubber mounted joints from the springs to the main kelderman pivot points. resulting in about a 1/2" total side to side movement.
if i have anouther air ride system installed, i would go with bags only. getting rid of all of the extra flex joints, thus providing more side to side stability. ie: less shifting.