I got the ii in March. To be honest I do so much manual focus that the cameras are nearly identical to me. The AF is supposed to be better on the ii and there is a firmware update I still need to do for it that improves it even more. My son has recently started mountain biking so I am going to go out with him this week some time to take photos for him.Didn't realise you had the mk1 and mk2 Z6. Apart from the extra SD card (which would be a must for me), notice much difference between them?
I found the AF on the original Z6 far better than my D800 so I'm pleased either way. I also don't use the tracking modes very often which is where the improvements have been in terms of firmware. I just use a single focal point and track manually. But I will play with some of the tracking modes when I go out with him.