SK 35-30 1400kV motor with the Custom RC Parts motor mount and a 9x6 APC prop is superb in the Supercub. Much, much more power, very smooth running, and the flight dynamics do not seem to be noticeably upset.
The new water rudder worked great- for a while. Then water infiltrated the housing and started shorting it out. I had to disconnect it after the first flight. Hopefully the servo will dry out and work again. If so, I'll try waterproofing it with some bicycle bearing grease and try again.