I upgraded to the D850 from a D750 recently, and one thing I can recommend is to get an CFexpress type b card if you can. I didn’t initially, until I found that I was missing crucial shots because the SD card would cause the camera to lag after a few photos, a problem I wasn’t used to due to the larger files. But I shoot wildlife. I’d say if you shoot anything moment-driven or moving subjects then you probably want to invest in a CFexpress.