I flew my 1st Formosa with stock motor but had to change to 6.6 gearing with 12x6 prop to get some decent performance and that was with 8cell nimh pack.
For my current (3rd) Formosa, I'm now using a himax 2025 with 4.4 gearing and 9x6 prop. 3 cell 1320lipo. no problem with vertical with about 30 oz thrust and a 16 oz airplane. it gets out of sight in no time. Great little airplane.
I'm going to fly the Formosa II with same motor but the 6.6 gears and 12x8 prop, It should be ready next week.