@ChadS I am assuming you are comparing just the 70-200mm using a cropped section, and not the 100-400mm at 100-200mm. At 100-200mm I thought the 100-400mm was weak, and I think the 70-200mm would outperform the 100-400mm at anything close to 200mm. I found my copy of the 100-400mm did a good job at 300-400mm. It seemed to have a sweet spot at 320-350mm. However the IQ was not so good that it would hold up to a large amount of cropping, of course I say this from my perspective and no one else’s because how much you can crop really depends on the final use of the pic will be. I think as far as cropping goes the 70-200mm will give you more usable image to work with, but definitely not enough to crop a pic to match the IQ of the 400mm's framing.

@Neuro, A quote from Arthur Morris when someone asked about selling their 100-400mm and going strictly 70-200mm F2.8L II with TC’s. “I can never know if anything is “worth it” to someone else.... I do know that the 70-200 II is far more versatile than the 100-400, far more rugged, and, in the right hands, will consistently create sharper images. I recently sold my 100-400 and will be selling my last 400 5.6 when the person who borrowed it returns it. And I will likely be selling my 400 DO soon....” While the charts do not support his claims at 400mm, the 70-200mm II deffinetly wins with the 1.4x compared to 250 and 300mm. I wonder if the real benefit that Morris realizes is in the superior IS system. I have yet to actually try the 70-200mm II with the TC’s to test out his claims in real situations. I was wondering if you have.