It is a tough question to answer in general because it also depends on the lens. For example, with a screw drive lens there may be a big difference because as Marc says, the power output is higher on the k-7 body-drive AF motor. With an SDM lens, there may be no difference, because the motor is in the lens.
Focus speed is all relative though, and while significantly improved from the k20d, it has a way to go I think. Has anyone else seen this youtube video of k-7 vs 7D focus speed? The lenses are not the same, but it does show that our mount has a way to go to catch up in the AF speed race. If I could ask for one thing to change about the k-7 it would only be a
significant improvement in the SAFOX. For the lenses, a ring-SDM. Then I would be really happy.
The Pentax mount excels in all other areas though.
[YT]http://www.youtube.com/watch?v=ngUcQUchHEU[/YT]