The Avistar is an excellent aerobat trainer, and I agree that you should go with the bigger engine immediately. I have an OS .40FP on mine and it is definitely underpowered for most aerobatics. A .46 BB engine would add a lot to the envelope, but I don't think it has the elevator authority for 3D. With a bigger engine than I have it will knife-edge all day, though. Saw one with a .46 and a tuned pipe so unlimited on the vertical.