I started with an Avistar. It's a 40 size trainer as well. I put an OS 46FX on it. It seems to be an easy engine to run and plenty of power. It really helps to have the extra power, it saved me a couple of times from a major crash. If you do go with a .46, you might want to run it at 3/4 throttle at max until you get more comfortable w/ higher speeds. After you get better, the extra power and speed makes it a lot more fun in my opinion. Good Luck and welcome to the addiction.