This may be common knowledge but even if it helps out 1 or 2 people it seems worth posting here.
When I first got my 5d3 I had gone through the manual and some tutorials on youtube and had settled on AF point expansion for my AF settings. I would go back and forth between 4 point and 8 point. My line of thinking was that a bigger AF area would give the camera more of a chance of being able to get focus on a moving subject. I was getting some lackluster results, maybe around 50% of my pics with moving targets would be in focus.
I was recently reading the Ken Rockwell review of the 5d4 and came across this little nugget of info:
"Specifically, like all Canons it's as fast as can be if you select just one AF point, but if you set AF Area Select to AUTO, then the 5D Mark IV doesn't auto-select or track among all the AF areas very quickly. This is in stark contrast to the 1DX Mk II, which auto-selects and tracks among all its AF areas pretty much instantly. In other words, the 5D4 focuses in and out as fast as every other camera, however the 5D Mark IV's ability to select among the AF areas by itself (if you use this feature as I do), isn't that fast."
After reading this I decided to try switching to a single AF point. What a difference! I'd say that I'm now somewhere around 90% of my pics in focus. Obviously you have a smaller area to work with so you need to make sure you do a good job tracking your subject with that single point but it seems to work much better for me. Based on what Ken is saying, this will help with the 5d4 as well but I don't have one of those to test with.
