but if I were you and you can afford to switch systems, I'd do it in a flash.
With the type of shooting you do, you do not get second chances.
If you can get 15 shots of your wife clearing each hurdle or crossing the finish line or landing in the pit and choose THE shot, you are much further ahead than choosing between a half dozen shots.
You do not have the option, unfortunately, of having the race re-run or the jump done over if your K10 fails to lock focus at all, either.
Sure- you can pre-focus on a hurdle or on the spot in the pit and get a few shots, but that's a lame alternative to getting a whole sequence in sharp focus from take-off to landing, isn't it? In fact, imagine a panoramic sequence of a half dozen shots of your wife leaving the board, launching into the air, then landing in a cloud of sand!
I'd do almost anything for a sequence like that if I were you.
Your shots are more important to you than my bird and wildlife shots are to me (or someone's studio shots, or whatever, too, I should imagine). You need to use the best equipment available now, and Pentax,
at the present time does not offer a competitive camera to meet your needs.
All this is not to say you can't or won't get good photos of your wife in action. Just that you would likely do better with another brand.
There IS a reason you don't see anything other than Canon and Nikon being used by the serious shooters at track-side...