I am relatively new to all of this compared to many of the folks on here. I am the type of personality that when I see something awesome, I obsess until I can produce similar results. Example in point, images by our beloved messiah (sorry for the blasphemy
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@Steve. The work in his videos and books has shoved me down the irreversible and expensive path of photography at a higher level. I have always enjoyed making a nice image, but not since young adulthood have I used much other than a phone. Not that great images can't come from some of today's phones.
@DRwyoming @Callie and several others that post on here also have a quality level for which I strive. Realistically, these folks have years and years of practice which the rest of us can only gain by years and years of such shooting practice.
Lately, I have been following a photographer Steve Matheis, out of Jackson Hole, Wyoming on youtube as he photographs Great Grey Owls. I had Santa Claus order his "Phantom of the North" book and read the entire thing on Christmas morning. The book, which was worth every penny uses his images and the text is by a wildlife biologist who is on a multi-year study of the Owls.
When I see other people's amazing captures and the stories behind them, it simply fuels my need to practice and hope to create something that I am equally proud of. So the point of all this rambling and related to your original post would be this:
Just like you, I see most of these folks using FX. The D850 in a high percentage of cases. It makes some folks think "Man, I gotta get me a D850". What I have learned and noted from my obsession while out shooting, even if just common or boring wildlife is that certainly there
is a difference in DX vs FX captures. But, that difference is such that it is difficult to put a descriptive word to. An increased "richness" is the word I could probably come closest with. The FX captures tend to just be creamier, smoother, and "richer" in some way. I shoot D500 and D810. HOWEVER, even with my opinion of being richer, the decision is almost always D500 simply based on the versatility of having an amazing autofocus and frame rate paired up with the added "
reach" of DX if I need it due to subject size. I find it very difficult to fill an FX frame for a high percentage of what I shoot. If I target larger animals that I KNOW I can get close-ish to, I pick D810 every time. What I often find is when I make that decision, something awesome comes along that is smaller and there I am needing to crop so many pixels that there was almost no point in hitting the shutter button. That being said, IF I was to purchase a D850 (grip required for 9fps) I could always use a crop mode for a similar capability and perspective of reach that my D500 produces.
But, all of that makes no difference, as practice, practice, practice is what will improve my images. All the while knowing that putting two high quality captures, with equal fields of view side by side, and not knowing which was taken FX vs DX I would challenge most viewers to get the guess right more than 50% of the time. Sorry, that got really long and rambly, but hopefully, it adds at least one usable piece of info for your thought process and decision for your particular type of subjects in the viewfinder.
Ryan
