One reason why #5 is often used these days on sailplanes is that the smaller tip chord slightly reduces the size and strength of the tip vortex. And a lot of the wing's drag comes from that vortex off the tip. The raked back Schumman style wing is supposed to be pretty much the best at reducing the size and strength of the vortex and this is why you see those raked back or even half elliptical crescent shapes on a lot of sailplanes.