I built and sold many sizes this year and I have found the perfect engines for larger sizes are as follows: 30 X 30 = OS32SX or the Magnum 36
: 36 X 36 = OS46FX or the Irvine 39 both using 4mil coro.
We use the Macs tuned system for all of our extreme PBF action. To use the larger engine that you are talking about, I would probably concider using the 11mil coro and though the weight WILL increase so shall the stiffness of the plane and you will save some $$$ on not having to use so many carbon rods to stiffen up the plane. I would go with a 36 X 36 with this material. Hope this helps. Bender