Pani ... I gone 6S and its a waste of time, the extra speed is not that much compared to the increase in watts/amps. Also the plane handles like a pig ... keen on that? If you want speed, get a new plane. The FJ is not made for speed. Many who flown her on 6S will never mention about the handling etc but only want to boast about speeds. Rockets are much faster to be frank.

Basically, because of the FJ's design you will be spending a lot of money to increase power so as to overcome the fuselage's innabilities.