having run both sonic and duo 3 motors in 17.5 boosted. The duo 3 has more bottom end punch and is fast all around. The Reedy is smooth on throttle input in the infield. I had to change a few things on ESC settings and gearing to keep the heat down and try to keep up with my old duo3 on the top end.
If setup right both motors is just as fast. To me the difference is the throttle feel.