Quote Originally Posted by neuroanatomist View Post
If 560mm was enough for me, I'd be interested in this lens. As it is, I'm usually using at least the 1.4xIII on my 600 II for 840mm f/5.6, and sometimes I go to 1200mm f/8 with the 2xIII.

I'm not sure f/4 (much less f/5.6) is optimal for sports, even with the high ISO performance of current FF bodies, in the 200-400mm range one often wants the additional subject isolation that an f/2.8 lens delivers.

I can see the 200-400/1.4x as the ideal single tele lens solution on a safari, for example. But then, it's also worth considering that a package consisting of a 1D X, 300/2.8 II and 2xIII is not too far off in cost from this new lens...
Good points as always from you Neuro! Thanks! +++1!
The Canon EF 600mm f/4L IS II USM with extenders version III are just phenomenal! Surely an excellent choice!
All the Best!
/C