Wondering if anyone has an opinion or comparison between a Canon 70-200 f4L IS with a TC vs. Canon 100-400 L IS?
100-400 Simply for the fast focusing.
2X has no auto focus, but the 1.4X does. I went the route of 70-200 with 2X and hated the choice from day 2!
100-400 w/ 1.4X is a dream and if cost is an issue, look into russian lenses for your rig.
I used the 70-200 IS f/2.8 with a 2X converter + a polarizer for two days at the Canon workshop Yellowstone last week and the autofocus was still very fast, I loved it; but professional photographers (the National Geographic type) tell me I would love the 100-400 IS.