Here is a Nikon D850 vs D750 vs D780 comparison that shows the highlights to help you for decision.

Nikon D780 ($2,296.95 – at B&H Photo Video/Adorama/Amazon) an update to the D750, uses 24.5MP BSI CMOS sensor with on-sensor phase detection and offers 4K video. You can find a quick review and comparison sheet between these cameras.
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https://www.dailycameranews.com/2020/01/nikon-d850-vs-d750-vs-d780-comparison/