I just went from Castle 2650 to a Trackstar 1900 motor and 1900 is way smoother. This is in a Tekno D8. The 2650 just was to much motor, especially on 4s. With the 1900 on 4s it still has lots of top speed and power band is a lot smoother. I started to run my 2650 on 3s but was having heat issues with esc. As for gearing, try that 17 out. Just check your temps like every minute to make sure nothing is getting hot.