I currently own both the 1D4 and the 1DX. The 1DX is a completely new animal and my keeper rate is now much higher for sports. The auto focus tracking is in a whole new class for the 1DX and I will soon be selling my 1D4 and getting a second 1DX.
I use several different modes of auto focus on the 1DX which allows me to frame my shots more accurately and more quickly than the 1D4. I also have the different scenarios programmed into the C1, C2 and C3 settings which allows me to change dozens of settings on the fly with one button (without looking up from the view finder). There are many other little things I have found that make the 1DX much easier (or better) to use than the 1D4. I have not yet tested IQ but I plan on doing a side-by-side comparison this week.
Also, my AFMA settings have been much closer to zero with the 1DX as compared to the 1D4 but that might just be my camera bodies and your mileage may vary. The higher ISO is very usable on the 1DX. For indoor sports I don't go above 4000 (5000 if I really have to) on the 1D4 but the 1DX allows me to go 16000-20000 without issues. Full frame is a bit different but bigger glass can help.
Forgive the ignorance but what does AFMA stand for?