The Nikon D850 is the "Bread n' Butter" model in Nikon's full-frame DSLR line-up. New to its predecessor D810 are a 45MP sensor that supports 4K video and a faster image processor (EXPEED 5) for up to 7fps in full resolution.
We generally recommend SDXC memory cards (64GB and more) with an UHS-II-interface and a SD Speed Class from U3/V30 or above, if you're using a Nikon D850. Especially during burst shooting, an UHS-II enabled SD card offers a significant advantage in terms of speed. If you want to get the most out of your camera, you need to buy crazy expensive XQD 2.0 memory cards.
Memory Card Comparison & Review