Have actually owned both their 58 and 66 inch Extras. Used an OS 60 for the smaller one and Super Tigrer G75 (and later YS91) for the bigger one. Standard servos on both. The larger one did require a little bit of weight in front. Mount your engine as far ahead as possible as the cowling permits. Both are excellent flyers as far as my skills permit. Havent tried hovering or such but verticals are superb.