So the SPi is actually stiffer than both of those? Which one is stiffer b/w those 2?
stiffness used in this context was referring to the relative dampening ability of the bindings since he was saying that the SPi's stiffness led to knee and back issues. The cushioning of the NRC/CAD style footbed is much thicker than the SPi's, that is what I meant. In terms of "responsiveness", the CAD has a slightly stiffer highback, and both use the same ankle straps, so the difference between the two shouldn't be huge