Speaking to a techie in the hangar at Boeing field he told me that the new 767-400 wing tip is the state of the art as far as drag reduction goes. Forget your winglets especially the 747-400, they are not very beneficial. 3-6% on the BBJ unless its very heavy then it tends to twist the inboard root of the wing negating any benefit. They are working on it though! But next time you see a 767-400 check out the last two or three meters of the wing, it's very different.