One of our better airo engineers was also a modeler and made some exeriments with symetrical wings. He would increase the thickness of the airfoil as the span increased. Typically an 8% thick at root and 12% at the tip. He said his gut feel was that it improved the landing characteristics a bit by delaying the point at which the tip would stall and allowed lower landing speeds but admitted this was purely his perception and he had no measureable data to back it up.