I agree w/ everything that has been said so far. I would like to attack this in a different way though
I for one cannot focus a rf camera faster the the xp1 can af focus.. Others i am sure much faster than i. If I acquire a new subject in to focus on w/ a manual focus camera, it will take me longer to focus then the af mechanism of the xp1. The shutter lag of either camera at that point is about the same...
The af technology in the xp1 or xe1 is about a generation behind right now as compared to what is available on the x100s.
I might be wrong, but it seems to me w/ the latest firmware upgrade, the cameras sensitivity issues related to horizontal vs vertical lives have disappeared. The main thing is still finding contrasty subjects to focus on. The problem still becomes one of available light where contrast is lower as light gets lower (af focus speed will decrease or may hunt). Again, compared to before, the latest firmware has made this a lot better.
The size of your af target box matters. Try changing it around to c what works best for u.
The fastest lens for af focus lock that I own is the 18-55 zoom. The slowest is the 60 macro. W/ the latest firmware I find all the other lenses in-between to be acceptable. The af motor on the zoom is different then the other lenses, not only is it quieter, but it seems to be more powerful.
Techniques from the rf world like pre focus to a spot and wait for the subject to get there can be emulated w/ the technique of manual focus and afl button as mentioned above or simply by using the focus wheel and manually focusing based on the focus scale in the viewfinder.
Anything closer then about arms length, for the xp1, u are better off to switch to evf mode for more accurate focus since the issue of parallex will come into play.
Good luck
Gary