RE: all diamond dust post
The 8x8 matches up well with this plane. I spent some time last summer clocking mine with a variety of props, and the 8x8 was right in there for all around flyability, launchability and speed. The 8x8 allows nearly a vertical launch if the plane isn't overbuilt and if you've got an engine there that can pull it's own weight. The best times were with the 7.2x8.6 [launched at 24,000]. If the engine doesn't respond with this kind of rpm when you go down in diameter, then you're better off playing with more of a sport prop, like a 9x6 or 9x7. It sounds like your combo will crank the 8x8 in style, though.