ORIGINAL: kbless7
I'm not sure if prop size is a problem. There are actually quite a few people who use a Saito 100 in their U-Can-Do 46. I personally think it is overkill. I'll look into the Saito 82.
You'll be happy with 82. You can use an APC 14x4w with it and it fits in the cowl easily enough. It is plenty of power for the 46, I hover mine with it at about 1/2 throttle. Also, as was mentioned, this plane isn't made for speed at all. Just fun flying / 3D type flying. I'm on my 4th one and love flying it.