I use the 1d X exclusively and I can't say I KNOW it will have accurate focus as I shoot a lot with lenses that aren't optimal AF wise, like the 50 L. But mostly I blame the lenses not the camera, because I am never at fault whatsover
I don't use One Shot and have accepted that Servo of fast moving subjects at f1.2 isn't going to be 100%, but I trust my gear enough to try ridicolous things with the AF, and very seldom is it completely off.
I always try to be better at focusing, trying different settings for different subjects all the time, and shoot a lot so I know where it's VERY accurate and where I need to blast off a few more. Using the 70-200 I would say it's 99,99%. In a situation where I can't afford to miss, I use burst to be sure.