Wow, that's a fast upgrade. Is there a reason you are sticking to DSLR and not moving onto mirror-less? I imagine it's due to lenses which I get but it seems like hardly anyone is making those anymore.
Simply cost to performance ratio currently. MILC is just so expensive still where the urgency for many to move to mirrorless has caused prograde F-mount prices to drop substantially.
The only current Nikon cameras to meet my needs in the Z9($5500) and the Z8($4000). My birding setup now is the D5 at $2100, the 300 2.8 vrii at $2100, and the 2xTC at $250. Of course all used prices.
Z mount stuff used is still like buying new, so not much discount there. I just watched a mint condition Nikon 600mm F4 FL on ebay sell for $5600. I wish I would have snagged it. 500 F4 FL's I see routinely for $4400 like new.
Although I do now see the Z9 selling for $4400 like new so there's that. The Z 600mm F4 is $16000 lol.
Also I just don't like EFV. Granted I haven't looked through any current models EVF so I'm sure they've improved since I was shooting the XT2.
Many claim that the DSLR still has an advantage in AF in certain areas like acquiring initial AF, busy backgrounds, and low light AF. The other reason
I choose single digit D line is they are low light monsters. There's nothing in the Z line up that compares shooting at higher ISO's. I also thought I read that Z's still struggle in low light for AF?
What interests me with mirrorless is complete sensor coverage AF, no AF fine tuning(tbh I've never done this on my DSLR's), eye autofocusing(although does this take some of the fun out of it?), and
in general just being newer tech as I'm kind of a techie.