My vote would be something in the 1.4 to 1.6 range. A 72" airplane for good aerobatic performance should not weigh more then 10.5 lbs. You will find howerver that the One design is not a 3D airplane. It does well for sport scale like aerobatics. If I was building this airplane I would be looking to a YS 120-140 or Saito 180.