Very much looking forward to the 1DX III as a Canon bird shooter. My current setup is the 5DIV with the 800 5.6, though most all of bird stuff was with the 7DII, a good camera, just a touch noisy in low light. I love that lens, and got it used at a discount when many were going to the 600II, and now there is the 600 III. My main concerns are locking on birds in flight, in particular when they leave the perch, and will it be able to hold on when I'm tracking the bird. Also shoot a lot of warblers too who move around a lot. I'm confident it won't dissapoint, just hoping we get a official announcement soon.