For my project, the biggest problem turned out to be the Reynolds number. Due to the already tiny wing, the even smaller chords at the tip would stall already at landing speeds. Because of this, the competition is using Hershey bar wings. Our profile is more than 20% better in L/D at landing speed with even more forgiving stall than NACA 64xxx while performing the same at cruise speed. Sometimes it makes sense not to concentrate on faster / higher to get the better product.