Hi, the 46FX and the newer 46AX are very similiar in performance(both very strong running and reliable). The newer version seems to have slightly more power and seems to have an even smoother idle than the FX but only by a bit. The engine would power the Decathlon nicely. Your radio is fine as well. The Decathlon is more demanding than a 2nd type plane. Its take off can be a bear unless you throttle up slowly and can then be ready to counter with the rudder when the torque suddenly starts to turn the plane. After this point, the rest of the takeoff is straight forward. I wouldn't suggest it if your only other plane was an LT40. Its too big a jump The plane is heavy for its size but is amazingly fast and responsive. These 2 points alone make it too big a difference from a trainer, never mind the touchy takeoff!! That being said, its a blast to fly if you can handle it!