Wow, old thread! I don't know if ARTF has even been around since 2006! [&:]
As said, this plane has been flown (and very well) with a wide range of engines, I don't think anyone would argue that the lighter engines would allow it to perform better at a wider range of speeds. It seems like a lot of people use DA 50's in everything these days, and granted, it is a great engine, but I still would put a lighter power plant on this particular airframe. Why add more weight when you can get all the performance this plane can use with a lighter engine?