I love the 85 1.2L II for indoor sports (volleyball mostly) b/c I can get action stopping shutter speeds and good IQ w low enough ISO's to keep noise at an acceptable level. I have used it with the 5DMK II, 5DMK III and 1Dx. The 1Dx does seem to help w the focus speed (non scientific assessment), but the biggest difference in these bodies for this application is by far the improvement in the AF system and ISO noise in the MKIII and 1Dx versus the 5DMK II. The big advantage in the 1Dx over the MKIII is the frame rate - I just get a lot more captures of the ideal moment at 12 fps. As usual, technique matters (and mine can always improve). With the 85, I tend to track a single player and not try follow the ball from pass to set to spike - the AF is really too slow for this to work in my hands. Other lenses (135 f2 and 200 f2) can be used to track the ball movement - assuming the photographer can frame properly to follow the action - the lens AF speed is typically not the limiting step with these. Overall, I have learned to work with the relatively slow AF of the 85 1.2L II and find it a key component of my indoor action photography. And - you have an awesome portrait lens to catch non-action moments as well. Tight portraits at f1.2 are just amazing.