- Like what you've got: Reconsider. The D780 produces better looking images than the D700, all else equal; and the D850 raises the pixel bar substantively. The real issue with going from D700 to D780 is the trade-off in body design; some favor the old design, though I like the new one.
- Dislike what you've got: consider upgrading. You really only have two logical choices if sticking with FX DSLR: the D780 or D850. Frankly, I’d say that really is only one choice: the D850 is more the camera you’re giving up than the D780. But you’re leaping a lot of ground here in pixels, focus, features, and more. Still, it’s the ground you want to leap: get the D850 if you need to upgrade. But I'd argue that the D700 user today should probably take a close look at the D780 or Z6 II: they're more of a performance camera than the D750 was, too.