Why do they have 3 to 1 or better thrust to weight ratio on the 40-50% aerobatic planes, that would seem like a lot of unnecessary extra power - NOT. You fly the plane on a very small throttle setting, but you often 3D it on as much as you have available, and for some maneuvers, you need alot to do it well. I know a YS91 will hover this plane, but will it put enough air over the elevator to bring it around fast enough in a waterfall for my taste? NO. I bet my plane, with the YS120SC, and tail weight will fly as slow as somebody elses with an OS91 4-stoker or 2-stroker. Yes, I do advocate that every ounce saved on a 3D plane makes it a better 3D plane, but in this case, the load per area is so small, even with a YS120/140, that it'll still "float", or have a light feeling.
DKjens