CAREY ROSE, DPREVIEW:
We took particular notice when, last weekend, he pitted his new Nikon D850 against his Nikon D5 in terms of autofocus tracking. (What can we say; we're nerds.)
But why even bother? After all, the D850 and D5 purportedly have the exact same autofocus hardware—performance should be virtually identical. In fact, in our conversations with Nikon, we were told that the D850 includes an additional processor to handle autofocus calculations, just like the D5; they also claimed this processor was omitted from the D500.
More importantly, we were told flat out to expect 'D5 levels of performance' from the D850.
Read more, and take a look at the video, from here.