I have a Hangar 9 Arrow (which is a pretty similar airframe to the Avistar) with a Magnum .46. I've used a 10x6 2-blade and the plane flies well. I've also used an 11x4 2-blade and it flew OK, at least until I put it in the ground (but that wasn't the prop's fault). My guess is you can use a range of 10x5 to 10x7 and/or 11x4 to 11x6 and be OK.

I've also used one of the Evolution 3-blade props. While it would get the Arrow off the ground, in the air the plane didn't feel as "crisp" as with the 2-blade props. On the other hand, it seemed the plane would land slower due to the increased air resistance of the 3-blade. At some point I'm thinking of trying a MA 3-blade just to see what happens.