I've used an over square prop before and it worked really well. It was a 9x12 Grish racing prop that I fly the Jepe Spitfire with. It can run at low rpm and still makes that plane do 130+ mph.

Now these props are a really a big trend in speed planes, but prop manufacturers are way behind and there's really only one or two guys from Europe to buy them from right now. If they don't have what you want, then the only other thing you can do is make it yourself! I've made props before, so that's what I've been doing for the last couple weeks.

On Feb 12, I tested a 10.5x19 on my Flash hotliner. This plane is extremely well behaved and offered a great testbed since I can launch it without even running the motor until well after the throw. The only drawback is the light construction on the wing. I don't dare make any sudden moves with the motor running. I don't have any real data yet other than what I saw with my eyes and it seems really good. The prop runs very quiet once the plane has accelerated to the speed of your throttle setting. These things make quite a bit of noise at first because they are stalled. Even at 1/3 throttle, speed was high enough to worry about breaking the wing if I made any sudden moves.

Something I want to try out. I'll use an EF-1 plane to test it.