I don't know about the AF speed of the K7 as I have never tried it but I personally feel that the AF speed of the KX is not as fast when compared to its Canon and Nikon equivalent. I tried my friend's 500D and it seems to focus faster with just the kit lens compared to my KX with FA35. I tried taking a dance performance recently with the DA70 and it has abit of difficulty in focusing and catching up with the action too.
I remembered when I was using the D80 last time with 70-200 F2.8 and 18-200VR, I didn't encounter such problems. The focusing is faster and more accurate when taking events. So I guess Pentax AF speed is still abit lacking when compared to C and N.