I've not shot any motorsports, but one thing I've noticed with the x100 and, to a lesser extent with the XT1 is that if you know that you'll be using a smaller aperture (e.g. f8), then setting that on the lens seems to speed up the focussing. I think it's a depth of field thing - in auto aperture it will try to get best focus with the lens wide open, whereas it can take advantage of the depth of field when you set the aperture to get "good enough" focussing. I'm not sure how well this would work with the X-E2 (and I'm not sure it's not a little bit of placebo with the XT1), but it definitely helps on the x100, so could be worth a try.