If it helps, I drove GX 460 Premium, Premium Plus and Luxury back to back to back multiple times and really didn't notice much difference between the ride and handling at all. I think the Luxury is probably a little softer, but that is offset by the larger wheels and smaller sidewall, and the Premium/Premium Plus have smaller wheels with more sidewall, which lends a squishier ride. I think the net impact of each is extremely similar.
I bought the Luxury because I wanted real leather, Mark Levinson audio, and liked the wheels more. Even the Sport-Normal-Comfort suspension settings are barely noticeable.
I think the big difference with the AVS is with towing or off roading and being able to raise/lower the suspension.
All of that is GX 460-related, so just not sure about the 550, but happy to share if it gives you something to think about.