I'm stuck in between buying both the 400 f/5.6 and 70-200 f/4 or just the 100-400. The reason that makes this hard is because I'm going to use them both mainly for surf photography and its nice to have the zoom range but i dont know if it would be a good idea or worth the trouble to switch in between the 400 and 70-200 everytime i wanted to zoom. I know the image quality on the 400 is better than the 100-400 but does anyone have both lenses and is it a dramatic difference or what? any sugestions, comments, or advice is appreciated. THANKS!