catfishjohn: You really don't need an engine that big. Decathlons are not met for speed; they are not racers. Like a Cub, they are a short-coupled high-wing taildragger that stears with the rudder and flies on the wing rather than the prop. I have one that's similar, only it's a discontinued Lanier Citabria with slightly higher wing loading than the Phoenix Decathlon. The .46 AX will pull it around just fine, and it also has a very long glide ratio considering that it's not a sailplane.

NorfolkSouthern