Unless you wanna shell some serious money (like, 1D or D3 money), I'd have to suggest you pick any camera you feel comfortable with and learn its quirks. Even then, people have complained about the AF on some of the more expensive cameras.
It really boils down to technique in the end. Once you get comfy with whatever camera you choose, you could probably nail the shot you need. I find that I am getting more comfy with using manual focus lately, not because I don't trust my Pentax's AF (which is pretty darn accurate), but because I like to shift focus much more quickly. I've read people recommend manual focusing, too, and maybe it's something you could look at.
If you could wait until Photokina, maybe Pentax has something to show in the way of a new higher-spec camera (which I'm sure will contain a new AF module).
You could also try to ask help in improving your technique with some of the resident action/birding shooters in this forum. There are quite a number of them here, and they can nail the shot even with *only* 3 FPS or even a much smaller buffer as with the K100D.
That said, if you really feel that switching systems is necessary *now*, then by all means go ahead. I'm not one to hold back someone who have need for better action photography performance (and you certainly do need it).
I suggest you rent out cameras and see which one's to your liking. Good luck in your decision and congratulations on your wife's achievements. I sure as hell can't run fast if my life depended on it.