Regarding Rapid Rise, a lot of it depends on your riding style, technique, etc. I like Rapid Rise for mountain biking for the very reason Shimano introduced it, I guess because I don't seem to have a problem easing up on the pedaling torque for an instant or two when shifting, even when in urgent downshift situations off road. Overall, for XC mountain biking, I like Rapid Rise better. But different strokes for different folks. I will say I'm glad Shimano offers mtb rear derailleurs in both configurations-