I sold my much loved D5 D4s with absolutely no regrets and bought 2xD850 cameras.
I have a grip on one and enjoy 9 fps which is plenty most of the time, i do rent or borrow a D6 if and when its a really lower light challenging shoot, but its rare now.
For me the benefit of the D850 was 45mp 9fps allowing very good crop ability, i could use a 70-200FL which is super sharp and a light lens, with 45mp i could crop the image and be on par with a 300mm- 400mm lens on a lower res camera, something not as tolerable with the previous cameras. I hardly touch a TC now.
The 70-200 FL is unique, its the best Nikon has ever made, it handles a 1.4 TC III or II brilliantly, for me there is a difference between the TCII and III.
Its hard for me to go back to a D4s D5, i do love them, adore the D6 D850, getting used to my Z9.
For me on the D850 I had 45mp corp ability, 9 fps, back light sensor, stunning image quality, excellent all round performance that also grew the legs on many of my lenses through excellent crop ability, something i would choose over using a TC.
I sold one D850, keeping the one with the optional grip, i can leave the grip off and travel with that D850 so gladly.
I then bought a Z9, for me the Z9 main advantage is the focusing system, optional FPS, 45mp, crop ability, true silent mode, backwards compatible with DSLR lenses.
Option to grow into new small lighter glass, makes any DX camera obsolete as did the D850, the Z9 is basically the brilliant D850 on Cocaine.
From the left field, only and totally absurd, Maybe consolidate everything you, ditch all you have, build again from a blank canvas with a simple system that eliminates the use of Tcs, gives you access to newer glass options in the future, which may allow you to focus on and enjoy more your photography with newer technology, maybe not?
The industry is going light small powerful and up in resolution, yet is still backwards compatible, for now, once you enjoy the use of 45mp its hard to pick up a D4s D5 again, i mean i love the D5 miss the D6, but am so happy with the D850 as back up to the Z9 i like.
The Z100-400 is a great all round lens, the 200-600 coming i hope it will be small and light, i really hope similar in size to the Canon 100-500.
Any way i have no simple solution for your needs, but maybe my rambling will excite something to think about, that may or may not help...........
Only an opinion
