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
Sorry I did not realize that. I agree though, SPI=more responsive while NRC and CAD are more forgiving with CAD being slightly more responsive. In my experience the thick footbed does not really take away from performance but makes the ride super cush, supportive and comfortable.