N1EDM,

I ran some numbers on this site:


http://brantuas.com/ezcalc/dma1.asp

Go there and plug in you batteries, motor, and prop and see what you come up with. It looks like the 4120 will handle up to a 6 cell Lipo, and 70amps. The way the numbers look, you will probably want to go to a 5 or 6 cell lipo. The load of the big motor brings the volts of you battery down to less than 14 under load. So you even with 40 amps, it says you will pull mid 400's for watts.

Here is an example:
16x6 APC prop

49 amps

584 watts

You could go this route and have a very nice sport plane, but you would be lacking power for 3D. A 5 or 6 cell would make a huge difference in power, but I don't know that you would want to buy more batteries. Maybe the plane will come out lighter than I think. It looks like your motor and batteries will wieght about 2 pounds. That leaves you 3 lbs for speed control, reciever battery, and plane. Run the numbers, and see how you do.

Adam