I received my copy yesterday after pre-ordering this lens a month earlier. I mounted this lens to a Canon 1DX2 camera body, did my AFMA calibration and was ready to go. I purchased this to shoot indoor action sports (mainly soccer). I was previously using a variety of f/2.8 lenses to cover this, but at ISO 16000+ in a dimly lit venue, I needed another solution. The EF85 f/1.2 had auto focus tracking that was painfully slow and unusable for indoor sports, so I was excited for this to be my solution given the improved auto focus.
At f/1.4, I was able to shoot the same venue of indoor soccer at ISO 2500 and still stop the action at 1/640 shutter speed, which was great! However, at f/1.4 the images were softer than I am used to. Unfortunately, most of it had to do with the speed of auto focus tracking. While very close to the best Canon L series lenses (no comparison to the terrible EF 85 f/1.2 auto focus), it still falls a bit short. Don't get me wrong, it's not at all like the prior f/1.2 version of this lens which I couldn't even use in a setting like this. With this lens, I could track subjects on AI Servo mode with reasonable success (about 70-80% keepers). However, to put the auto focus in comparison to other Canon lenses, it does not focus as fast as the EF300 f/2.8 IS II USM lens or the EF70-200 f/2.8 IS II USM lens, both of which I was previously using to shoot indoor soccer in this same venue.