For those curious, I made a final call about the camera. I decided to keep it, because even though it isn't a huge upgrade, it has enough things that make it worthwhile for me.
- Dual CFExpress cards mean a much higher fps. Remember that the 1Dx2 is 12 fps if dual writing to CFast + CF, so the 1Dx3 at 16 fps is noticeably quicker.
- When I compared images from the same subjects, ISO, shutterspeed, aperture, and lighting, I did see that the 1Dx3 images are sharper. Is it a huge difference? No, but there is a difference.
- Also when I compared the images, I did see a noise improvement in the 1Dx3. I didn't see the 1 stop improvement Canon claimed. It's maybe a half or a third of a stop, but it is better.
- The AF selection button is amazing, especially as I get used to it. Once I changed the custom button settings, I can use it to change AF points without pressing another button first. I was able to very quickly change AF points using it, and it pretty much removes the need to have buttons map to two different AF points.
- AF does lock on better. In general I'm finding that the AF algorithms have changed, so some things that worked on the 1Dx2 don't work as well on the 1Dx3. I do believe as I get used to it, though, that overall the AF is improved.
- Supposedly longer battery life. I haven't verified this, but if it's true - then nice.