I don't have a 40 LA, but 11x6 is at the top of the recommended prop size. If you go to a smaller prop diameter, such as a 10x6, the engine will be able to turn higher RPMs, which can translate into higher speed. Staying at the same diameter, but dropping to a lower pitch, such as an 11x5, will also let the engine turn at higher RPMs, and should give you shorter takeoff distances. In short, buy a few props such as 10x6, 10x7, 10.5x6, and 11x5, and see which is best for what you want.

Something to remember is the .40 LA is a good, but basic, engine. Don't expect it to give you unlimited vertical. If the props don't provide the performance boost you want, there may be nothing you can do other than upgrading to a more powerful engine. However, there's alot to be said for an engine that's not overpowered. Being forced to fly the plane on the wing, instead of on the prop, can actually improve your takeoff and flying skills.