John Sherman writes up an extensive comparison of these cameras photographing everything from Buffalo to Prairie Dogs to BIF in an article for Photography Life comparing them with lenses up to 800 mm. He spends considerable time explaining how to crop with various bodies to get better results. His writing style struck me as being unique.
http://photographylife.com/nikon-d4s-vs-d810-vs-d600-for-wildlife-photographyBill
No real surprises there for anyone who has shot wildlife with full frame Nikons.
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