Nice write up FE....I had the Michelin XPS RIBS on a 5er that had a GVW of 14,000#, loaded to a little over 13,000# and a Pin weight of 2500#....Those tires were on that Coachman Somerset three slide 5er longer than "I" would have kept them on there and I towed all through the mountains of NC,SC,TN,Va and WV for a couple of years...a very good friend of mine bought the 5er when I got he one in my sig. He towed out west and put a PILE of miles on those RIBS and had them for over 6 yrs when "I" recommended he should get some new ones..he did and purchased four more Ribs...experience speaks volumes...
I would highly recommend an XPS RIB, or the tire that Me Again mentioned. I recommend the right tire be used in the right application and for the OP's 5r, the "E" rated RIBs along with several others would work great for him.
To the OP, I too wouldn't recommend using the Michelin LTX M&S tire either.