Great picutres! I'm going to differ from Stoo (his boat has the heavy hypalon) a bit on this. I've got boats with both material thicknesses. The 1670 dtx hypalon is 15% heavier (than the same surface area of 1100 dtx hypalon), yet has more than double the tear resistance.
Assuming that the weight of the fabric alone accounts for at most a third (and probably less) than the total weight of a RIB with fittings & motor (even with an empty fuel tank), the heavier hypalon wouldn't add much more than 5% to the total weight of the boat.
For example, suppose you have a rib that weighs 600 lbs without the motor, and 300 lbs of it is 1100 dtx hypalon, the rest is hull & fittings, then add a 300 lb outboard for a total weight of 900lbs. If you opt to go with the heavier hypalon, it only adds another 45lbs (300 lbs x 15% = 45 lbs) onto a 900 lb boat, which is a 5% increase.
Given that you will have a much tougher and more durable tubeset, I believe that the heavier hypalon is well worth the extra weight and cost.