Stiffness: All of the NX2 bindings are very similar in terms of primary flex (the base, heelcup, lower 2/3 of highback are identical on all 4 NX2 models). Only the top 1/3 of the highback and the strap changes between models. The top highback panel in the RS is carbon and is obviously stiffer than the others. The top panels in the other 3 are different but this is a very subtle change to notice when riding. We are talking about variations in the top 2.5 inches of the highback.