Having both cameras for some time now I would agree with something bdunbar wrote earlier in this post.....the 1dx shadow recovery is noticeably better than the 5d3 at higher ISO's.....and the AF system is better for catching action/movement... no doubt about it.
The extra mp's of the 5d3 do come in handy in good light if your subject isn't moving much, and if that is the only type of wildlife photography that you're doing then yes, the 5d3 would be better.
But...I've seen a million shots of a bald eagle or bear or wolf...etc, just sitting still in good light...cropped in close. My point is that those shots get pretty boring pretty fast.....BUT:
1. If you saw two bald eagles fighting in mid air (as Gary samples has shown in the 1dx sample images section) you would want the speed of the 1dx
2. If you saw any big cat trying to capture prey...you would want the 1dx
3. If you saw a mother bear caring for her new cub in the shadows of a forest....you would want the 1dx.
4. If you saw two alpha timberwolves fighting for control of the pack at sunset...you would want the 1dx.
For me, these are the great wildlife photos/moments that I would want to capture because they are so much more interesting and special.....and the 1dx simply does it better.
Interesting thoughts. However, the 1DX might not be able to achieve autofocus in very low light. Depends on the situation. The 1DX is no doubt the best autofocusing camera in the world, overall. Makes me wonder what the future holds.