Hindsight being 20/20 I would go with a Saito .91 over the Magnum or OS, since it is so light. From what I have seen from the Saito .82's, they are real powerhouses as well and should work great in this plane. I had to mount everything in the tail with the Magnum .91, since it weighs nearly 23 ounces. With the Saito's you would have much lower wing loading and could have a better choice for where you mount the battery and servos. I am thinking you may be a little disappointed with a .40 in this. It is a pretty large plane, with extra drag from the wing struts and tall fuselage.