I would say you would be better off with the cap580 and the OS70, (I would run the YS63 more power and it's only a $30 difference) That setup will perform much better than the extra 90 with the fs90, the 91fx may be ok but I really like the 4 strokes on an aerobatic plane. The cap with that combo should have very good if not unlimited verticle. I can't really comment on the 90 with the 91fx, but I don't think you'd be happy with the 90fs, it's too low on the recommended power and verticle will suffer.