« on: July 06, 2013, 09:21:26 AM »
I'd probably get rid of your 100-400 though, as the 70-200mm f/2.8L IS II with the 2x III is better at 400mm; especially on a 5D III.
My 100-400 @ 400mm is better than my 70-200 II + 2xIII @ 400mm. Not massively better, but noticeably better. That's also consistent with TDP's ISO 12233 crops.
Not only me saying this, but Arthur Morris (birdsasart-blog.com) says the same thing and gave the same advice. The 70-200mm II even with extenders has more resolving power. Maybe something wrong with your 70-200.