Upload & Sell: Off
Mark, your ballet shots are very nice, third would my fav.
I think they may have benefited from a higher ISO setting to yield a faster shutter speed. And maybe one notch narrower on the aperture for more DoF. Most lenses, even some of the very best ones, gain a little sharpness when moved away from the extreme wide open setting. At ISO 400 & 500 you are not using your MkIV to best advantage in low light situations.
As for the 85L's focusing ability when shooting moving subjects - I think it did well in your ballet shoot but that wasn't a very challenging test considering that the movement was lateral, and that the subjects are very well lit by spotlights against a relatively dark background. Although the ambient light level in the theater is not bright - it's not the same type of "low light situation" a sports shooter would encounter in a dimly lit high school gymnasium. Try shooting a HS basketball game, or a volleyball match, and you will learn a little more about the capabilities of the 85L. Your MkIV is very well suited for that task.