This review from Photography Life says it all; the conclusion being there really is no competition. I’m liking the tilt-screen, the illuminated back buttons, improved ISO performance and focus system, all making exterior night shots less of a shot in the dark.
‘There are very few areas where the Canon 5D Mark IV can hold its ground against the Nikon D810. Nikon has done a phenomenal job with the D850 and it really shows when one looks at a chart like this, since it highlights where Nikon was aiming with the announcement. Clearly, Nikon’s goal was to make sure that the Canon 5D Mark IV stays out of the competition, and as you can see from the chart, Nikon beats Canon pretty much on every major spec. It has a larger viewfinder, much better storage media options, an option to increase continuous shooting rate by 2 fps to get to a total of 9 fps, better flash sync speed, better shutter durability, better AF system, larger AF detection range, 4K video without any cropping, a tilting LCD screen, a far superior battery life, and a lower price point.’