Dog looks like it's having a blast though.
Yes he did.
Tried again today with the 18-55.
Some disclaimers first: I am not experienced with AF-C. I rarely used it before, even on my D90 where I was disappointed with it. My usual is AF-S with using DOF and predictive future position. On my D90 I used to get more keepers this way even for faster moving targets, such as kids, compared to AF-C.
On the XT-1 you need to keep the target in the center which is not that easy particularly with my subject from today. If far away and coming straight at you or parallel it's ok, anything beyond that becomes a challenge.
IF you are able to keep the target in the center AND it starts with a good lock you might expect more than 50% success with good conditions. Anything else will be worse.
I don't know if it's the lens but it doesn't often change the focus fast enough when the object comes close.
A big surprise was that it wasn't that easy to get the first shot in focus. Many times I think it related to the busy background. If that didn't happen it rarely found the dog by the time it came next to me.
For away targets can disregards foreground distractions, when they are close it is fooled often.
At 6 frames/sec you can reach the buffer easily.
Black dog on whitish snow is not that easy as it is really difficult for the camera to focus on the head vs the tail or the legs, it's just on big fast moving erratic black spot.
I don't have experience with a good AF-C camera to know what I should realistically expect. I'm still thinking because of this to give a change to D7100 or its successor.
I attached few more of the test shots.