You sure that the Cooper weighs 50 lbs? I had the AT3s in P285/70-17 and they were only 44 lbs. each on my scales. The 265/70 should go that much or less.
I never weighed my LT265/70/17 Cooper AT3's, I'm going by what Cooper emailed me when I asked them. Your 285's were "P" rated, and LT tires are heavier without a doubt.