I am signed up for a five-day trip through southern Ohio two weeks from now that focuses on photographing spring warblers. I am assuming that these will be newly arrived males on territory. For this kind of photography, what do people think the ideal focal length might be? Would the Nikon 800mm f6.3 be overkill? It focuses closer than the f5.6 version but it's still a lot of lens. Has anyone been on this type of trip previously? Any tips?