Thoughts on D850 upgrade from D810?

I've now used the new rig for 13 dives, with 16-35vr, 105vr, and 105+1.4tc.

Camera - definitely an upgrade, and you can see the difference the extra pixels make.   Autofocus is better, as expected, but also different (also as expected).   It does focus faster, and in lower light, but it also jumps off focus faster.  I've changed a couple of settings to slow down the jump-to-new-subject speed.  Auto white balance is definitely better too, but that only makes a difference in shallow water.

Housing - new housing is heavier underwater and is negatively bouyant compared to the D810 rig.  I may add a float somewhere.   I've mostly gotten used to the control changes, but I think the controls on the D810 rig are positioned better.  Changing either ISO or white balance is a bit of a pain now.

Focus light - once gotten used to the controls (2 buttons do all), it's been an unqualified improvement over my Fishlite V24.   More light, and battery looks like it may last two dives.

Teleconverter with macro - a qualified bust.  I like the extra working distance a lot - but the sharpness has dropped too much.   I've taken it off after 1 dive.

Sea and Sea Internal Correction Lens - this filter goes on the 16-35 zoom and is designed for the 'Sea and Sea 240mm dome'.   I have a 230mm dome, and i have to say this filter is the real deal.  It very definitely sharpens up the corners as advertised - like stopping down another two stops or so.  Now I can shoot at F5.6 with reasonable results, meaning I don't need nearly as much light or ISO.

Overall, a noticeable improvement to me.