I would (and might) buy the D850 over the 5DIV for a few reasons:
-flash sync 1/250 vs 1/200
-BSI CMOS sensor
-51 frame buffer vs 21
-native ISO range is wider
-better AF with wider detection range
-focus peaking
-focus stacking
-1.0x crop factor for video
-double the battery life 1840 vs 900
-flash sync 1/250 vs 1/200
-BSI CMOS sensor
-51 frame buffer vs 21
-native ISO range is wider
-better AF with wider detection range
-focus peaking
-focus stacking
-1.0x crop factor for video
-double the battery life 1840 vs 900