Interesting that you put the D850 and the D4S side by side here. Some people might consider this as being offensive
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There are a couple of threads here in the meamtime that dealt with your question - directly or indirectly, e.g.
D4 yes/no
D4 to D5, Back to D4
D850 vs. D5
Taking a look will tell, that the D4S can definitely be a good idea, if you look at low light capability, but only if you can live with other drawbacks like resolution or modern features like focus stacking or enhanced video capability.
All I can say I just sold one of my D750 and replaced it with a D4S as my prime camera sitting on the long lens for wildlife because of burst rate, buffer and low light tolerance.
But I am in the lucky position to be able to choose the camera depending on what I want to do. If you look for working with one camera - or one type of camera - the decision cn be more demanding as you might have to make a compromise - or two.
Just a few things relating to the threads mentioned above.
- Providing the camera is not too old from the in-camera computing technology the the pixel size is still the prime criteria for low light tolerance. It is just physics.
The effects might be partly coverable by more advance in-camera software, but it can't be completely compensated unless you can take use of a totally new sensor technology.
- High resolution gives magnificant potential for capturing detail - and for cropping in case you can't fill the frame (sorry @Steve). But it requires decreasing pixel size and this again works against low light tolerance. Also with higher resolution your entire system becomes more sensitive to motion blur in the sense of making it visible. @Steve has provided an excellent explanation in one of his ebooks which proved itself to be true for me right when comparing the behaviour of my cameras (16,6 MP FX vs. 24,3 MP FX, 24 MP DX)
- I forgot about that one in the past as well, but buffer and burst rate can save your a... and since I am able to shoot with 11 fps if needed I know what @Steve meant when he said something like having the choice to get the perfect moment.
- The follow-up investments should not be forgotten. There are many people out there whose computer, storage and backup system will start to wave the white flag when it comes to storing and processing considerable amounts of 45 MPixel raw files.
I might be a good idea to work your way back, finding out kind of resolution you really need for what you want to do and then look from there for the camera that suits your other needs most like low light tolerance. Assuming that you want to spend as little time as possible with post processing the first step is always to avoid creating noise in your images in the first place.
Currently I am on the move from one processing software to another and from the tests I was doing it is not only the amount of noise that varies from camera to camera, it is also the kind of noise, where one is easier to get rid off as the other.