Quote Originally Posted by HDNitehawk View Post
I'll give a few more thoughts.
The 70-200mm has 4 stops of IS. The 100-400mm has 2 stops of IS. Low light this will be important.
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4 stops @ 200mm. I wonder what it is with 2x so you are @400mm.
Low light is important for hand holding but also for subject movement. IS will not help with subject movement. Using a 1.4x giving an f4 @280mm will probably be better than 300mm @ f5.6.