1.1 and 1.7 refer to the weight (strength) of the fabric used. A DL has more strength at the same fabric type than its SL equivalent. Per Brandon, the fabric is far more likely to stretch as you near its weight rating than it is to actually fail, so you make your choice based on whether you want a little bit of sag to develop (most don't) or you want the lay to be as flat as possible. The DL also has an advantage if you want to use a pad because you can put the pad in between the layers so it won't shift on you during the night. The suspension is completely independant of fabric choice. The adjustable webbing is about as simple as it gets, but whoopies are almost as simple and a little lighter. You can't go wrong with either.