I wish somebody would make an 18" rear in a 140, 150, or 160 with at least a 70 profile rated for around the 900 lbs mark, but nobody does!! There is a huge market out there untapped for that tire.
This was one thing I didn't think of when changing the rear tire out to a 160. When we travel I usually have a tour pack "FULL" and tow a trailer. Now I am worried about towing the trailer so much that I took off my trailer hitch.
If they do come up with a 900# tire I will reconsider trailering with the tour pack again.
B...the 160/60x18 is rated high enough for the load, but according the the Metz rep I talked with, it's the amount of air volume in the tire that is the problem. I'm sure they are overly cautious in their recommendations because of liability, but he says because of the smaller air volume, the tire gets hotter and will wear quicker...the stock 16" tire is a 90 profile.

Do you know anyone else running that tire who could report on tire wear? I guess what he's saying is the profile of the tire makes a difference in how quickly it can dissipate the heat generated with a loaded down rear end.
I figure my bike in present configuration (all the chit I've hung on it), wet, probably weighs in close to 900lbs...the stock 402's are rated for 908 rear and 772 on the front, so let's just say a total of about 1600 lbs, so that leaves 700 lbs for load, though the bike does have a maximum GVW less than that. I figure the two people are going to weigh (in my case) 300lbs or a little more, depending on what we're wearing...with full leathers on, we're probably closer to 350+. 100 lbs of other chit on board, and I'm pretty damn close to the GVW, though the tires might handle more.
I was wanting to go with the same rear as you, and the 19 on front, both radials. But the 19 front is only rated for 557lbs...

So, I'm going with the 140/70x18 front which is rated to 667lbs, and sticking with the 16" rear 140/90, rated to 887lbs. That will keep me well within the tire ratings.
Like I said, I'm sure these tire companies rate their tires very conservatively, so there's probably a wide margin for error.