An 11x6 might be just a touch heavy for your .40 LA, but an 11x5 should be a good match. It will reduce your top-end speed but enhance the plane's climbing ability just a bit.

A Tower Trainer .40 MkII and a .40 LA engine should be a nice flying combination. I think you're on the right track to maximize your flying experience with it while putting your Kaos together.