Thanks Mike. Yes I'm kind of fighting all the various trade offs just like you.
The AF can't keep up with these guys with large zone but it does offer one advantage. If you lock onto the subject you can then move the frame off to the side with hopes that the action will occur in the direction you've left the space since panning at the speed they are going is for me, mere mortal, impossible. Today my idea is to set up the tripod and try some 4K video and frame grabs.
There also is no hope of me getting this action as close as required to allow ISOs like 12500. At 800 mm, I'm cropping to increase the size of the subject. This shot was more forgiving by luck, auto ISO was lower. The lighting is so variable that I'm auto ISO
Yes, Riley whatever I may be able to post is nothing but luck - well, coupled with perspiration and aching left arm muscles - close to tendonitis.

This is totally outside of my ability! O course I won't tell my friends around here that.
Jack