Most flyers trying the LA 40 seem to overprop it.  It does require a smaller prop than the 46, around 11/4 or less, or the new 3 blade Master Airscrew 10/5, maybe trimmed a bit.  The 40 looks like it has a bit higher stock compression than the 46.  It usually requires adding gaskets or enlarging the head bubble, where the 46 often will run OK without those changes.

When a maker bores out a case to fit a larger sleeve the ports on the larger bore usually end up being relatively smaller than on the smaller engine.  Makes the engine run more in the classic stunt style like the 46. For max power the ports always end up taking up virtually the entire circumference of the sleeve.  The 40's ports are relatively a bit larger than the 46, making it tend to be a bit peakier, slightly higher rpm engine.

Phil's observations as usual are spot on. They square with my observations, in any case. LA46s usually sound fat and happy. They loaf and pull. Or they can be tweaked leaner, if needed, to pull a plane with a thick airfoil, or a 40 sized plane on the heavy side. I've been frequently surprised at how well they run out of the box. Even for less experienced fliers not skilled at tuning in a stunt run. When compared to the 40, the 46 seems more tolerant of different props. Also, the needle setting is wider and less critical.