I would add that I went with the 50mm ones out of concerns/unknowns about road surfaces, as well as wanting to be easier on my wheelset for my trip.
When I ride 1.5in regular marathons, they do roll along more efficiently than the 2 in supremes, so Im sure 1.6 supremes will be even more efficient than my marathons 1.5, but you have a whackload more weight on your bike and wheels than me....so this comes back to wondering if wider would be better for you.
but hey, if youve used 35-40s before with the same conditions, then at least you know how your wheels holds up,but then thats up to you to know what works and what doesnt with such a heavy weight on your bike if you go with a ton of load.

good luck with your decision.