I put a ys .63 on mine (my first 4 stroke). All I can say is WOW!!!

It will do everything with that size motor (and it balances well, though you may still have to add tail weight, move battery, etc.). I usually fly around 1/4 to 1/2 throttle (yes, even 3D stuff).

Go back to main page and do a search on Global Freestyle, you will find several threads and comments on people using different engines. Also check out the review on the main page, its pretty good.