I ran the thrust numbers also. The 11.5x4 ends up flying the plane better. The engine doesn't have to work as hard to pull the plane. Overheating is a major concern with the Ucan DO. You may like the 12 inch prop better. On a close to 6 pound airplane you will find it just loads the engine down to much. I have tryed all of the APC' and always end up back with the 11.5x4 on a .46. The 12.25x3.75 will work much better on a lighter airplane. Just my findings. Good luck. Jason