Given one would benefit from the extra range-
So from what I've read the 70-300mm is as sharp as the 70-200mm f/4 IS through 70-200 at the minimum, perhaps even further out. Also, while the 70-200mm is f/4 constant, again my understanding is the 70-300mm is f/4 up to 200mm.
So, even if the 200-300mm range is ever so slightly less sharp and is also f/5.6, since the overlapping range between the two lenses is basically the same I am not seeing any disadvantage with this lens vs the 70-200 f/4 is... Thoughts?