I have flown my US 40 with a K & B .61 twister and a ST .90. The model will handle the power with out any problems. I do use a four servo wing and I set my rudder and elevator servo's aft near the tail. It has very good vertical...and I liked the K & B .61 Twister best. It's a well made ARF and I would recomend it to anyone that wants a kick back model that is simple, but kicks serious tail feathers once airborn.
Soft and gentle landings always,
Bobby of Maui