So, having bought the Nikon D800 body a few years back then upgrading to the D4 last year I made the switch to an FX body with super fast frames per second and a seemingly endless buffer. I could rattle off 30 or 40 RAW frames in a few seconds and the D4 never slowed down a bit, keeping everything in focus and exposed the way I wanted. To be honest I have never used a better camera body and probably never will, it is a fantastic piece of equipment and I do not regret making the purchase. For sports events I do not think there is a better body available. Maybe the New D5
Having said that, I always missed the extra reach of the DX bodies I had used in the past. I decided to sell off the D4 while the value was still high and go back to the crop factor sensor in the Nikon D500. A DX body with 20MP sensor. Being able to fill the frame with a 20MP file has a huge advantage to always cropping the 16MP file of the D4 and ending up with a much smaller final image.
The D4 is certainly a better overall body but I learned a valuable lesson in the fact that I really did not need the Nikon flagship body for what I was shooting. Hope this info helps anyone considering new gear. Only get what you really need for the type of photography you do most of the time.