I am basically a still photographer. Apparently, my renewed interest in photography has created a reputation of me being some sort of photography guru. HA-HA 
So, folks with smartphone cameras have begun asking me to come and take pictures for them of this, that, or some other event. No weddings, just Little League games, and the like.
Shooting stills means using One-Shot focusing mode, which may not be best for moving subjects. So, I've been exploring and experimenting with AI Servo mode. Which, brings me to a question that I cannot answer.
Does it matter if I am using just the center focus point, or should I need to turn of manual point selection altogether?
So far, my experiments have been inconclusive. My shots are in focus, but I am attributing that to pre-focusing. I get much better results by pre-focusing, than when I don't. Keeper rate is pretty much the same with manaul AF point selection, no matter if I use One-Shot or AI Servo modes.
I pre-focus on a player, or where I expect a player will be: i.e.; focusing on the base ahead of the base runner. I can get good shots, like the above play at third base. [the shot has been cropped to remove faces and team information]
But, forget about refocusing on an outfielder chasing down a ball. The kid is running, so One Shot doesn't work out very well, but neither has AI Servo with only the center point, manually selected. Turing on all of the AF points, 9 in a 6D, results in the camera frequently focusing where it wants, not where I want it to.
I guess I am saying that it seems that I have not been able to have the camera actuallly track a moving subject. So, do I need to turn on all AF points, in order to make it track in AI Servo, or not? For me, I am having bad luck relying on automatic AF point selection to pick out the running kid in the outfield, instead of a background tree, or something.
"I just may look into that idea of a clean 1D Mk IV, ..."
Oh my, 
there is no camera that even comes close to the ability of the 1D Mk IV. None! It is second in line only to the 1Dx series. It is still the preferred camera by a lot of pro sports photographers. It is also a highly sought after camera for wildlife photographers. Professionals not wanna be's.
I don't mean to say the the 6D or any of the rest of all the DSLR's out aren't good and capable but none are in the same class as the Mk IV.
I have been toying with the idea of a 1Dx but at this point in my life, I don't see a great deal it has to offer me over my current cameras.
With the 1Ds Mk III's 21 mega pixel sensor, it is hard to beat, too. The only place where it falls short is in high ISO. If you buy a 1 series you will never touch that Rebel again. Probably not even the 6D. Once you go 1 series you will never be satisfied with a lesser camera.
