I upgraded from a 5D Mark II and absolutely love the 5D Mark IV. A couple of weeks after my purchase there were some promotions on free items like a camera bag, extra battery, memory card, cleaning kit, went back to best buy and asked them for the free items and they gave me all these items free no questions asked. A week after this, the price of the camera went down by $200 and again went back to Best Buy asking them for a price match. They gave me the $200 and price matched it. Love Best Buy!
As regarding the camera, the autofocus is pretty fast and when compared to my previous 5D mark II it is way better.
The camera can focus on lenses stopped down to f/8. I use it with my 100-400L II combined with a 1.4X TC III and no problems at all in autofocus and pretty fast. Love it for my bird photography.
I love the 2 slots for the memory card, one SD and the other CF. One can can be set to capture JPEG while the other set for RAW capture.
Also the 7FPS is pretty fast for action. I use it for capturing birds and wildlife and love it.
If you have not invested a whole lot on Nikon lenses and just have a 300S with a basic lens, I think it should be worth the upgrade.