I don't know about the extra 200mm, but if you are doing nature shots and sunset, then you might want to consider the 70-200 f/4 IS lens. The lens is SO sharp, even at f/4, sharper than the f/2.8 judging by Bryan's ISO crops, and the IS is newer giving an extra stop of hand-holdability (making the hand-holdability of the two lenses equal). Given that the subjects you intend to shoot are not moving (animal subjects excluded) and you may need to carry your equipment a distance to get to your shots, you might appreciate the reduced weight (50%) of the f/4 compared to the f/2.8 since you don't need the action-stopping f/2.8.


Good luck.