My Super Skybolt is pretty much like yours, with an OS 91 Surpass II and digital servos. You might want to try a Graupner 14x7 prop as it won't bog down the engine as much as the 15x6. As far as the CG goes, I believe that Great Planes is doing the Super Skybolt a disservice by publishing such a forward CG in its manual. My battery and receiver are in their stock location as per the manual with no lead up front and the plane flys beautifully. I learned this as I gradually removed the lead from the nose (the last 2 ounces actually just fell off). This is a model I would definitely replace if something happened to it. I can't say that about any other plane I own.