I just re-read this thread & I noticed something that I had missed previously. The question was asked if removing the dihedral will make the plane faster, & fourstroke replied -- "In terms of flying faster, it won't. In fact, you can argue that by straightening the wings, you actually increase their efficiency... hence you fly slower" -- this is not correct. As already noted, the lift vector with dihedral wings is not vertical, so only a portion of the total lift actually supports the plane. This results in a necessary increase in the AOA, relative to a flat wing, to provide the equivalent lift. The higher AOA results in higher induced drag, so the identical flat wing with the same available power will be faster. The greater the dihedral angle, the greater the flat wing speed differential will be. However, in reality it will probably not be noticeable.