That seems about right. 70-200 f/2.8 L II is still king of the hill in terms of IQ. The new 70-300L is a little better than the 100-400L, especially at the edges, but not "incredibly" better.
As someone that was considering the 70-300L but bought the 100-400L, I have to say, I am happy with my choice and a little disappointed that the 70-300L isn't sharper. Had the 70-300L been equal too the 70-200 f/2.8 II L in IQ (plus the weather sealing and faster AF over the 100-400L), I would have considered giving up the extra 100 mm and making the switch when prices on the 70-300L came down. But, unless Bryan (or someone on this forum) highlights something I am missing, I think I am keeping the 100-400L.
So, right now, the 70-300L seems mostly to be a good telephoto companion to folks with the EFS 17-55 or EFS 18-55 that don't want one of the shorter but faster 70-200 lenses.
EDIT:
For those interested:
http://www.flickr.com/groups/ef_70-300mm_f4-56l_is_usm/
Also, the "CR" guy made the following comment on a trip to Africa "If I could give you a bit of a hint of what I think about it, I’ve taken less than 10 frames with the 70-200 f/2.8L IS II and a few hundred with the new 70-300L. It’s not for everything, but it’s been great for a lot of things."
Still keeping the 100-400L []




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