I have two Avistar's with .40 La's, I'm running a 10x6 Master Air Screw on one and a !0x6 Zinger wood prop on the other. They both fly very well, I seem to get a little more speed with the MAS, and a little more pull (quicker take offs) with the Zinger.  I have tried 10x7, 11x6, 9x6, in APC and Master Air Screw on these planes. They just seem to like the 10x6 MAS and the Zinger better. I also have another Avistar with a Magnum .46 and it seems to prefer an 11X7 APC.  Don't know why this is, but it's just my personal experience from my style of flying.