My experience with the K20D is that it's
not quite noisy. In fact, Pentax turns off noise reduction and you can dial it up as much as you'd like. The trade-off, of course, is loss of detail, which is what you'll find in all these other cameras that are supposedly less noisy. Shoot raw, and you can coax whatever you want out of it. Here's an example:
This was shot at 135mm, f/2.8, 1/180s and
ISO 2000. The noise (wherever it is) doesn't bother me. Also, in addition to being dim, the action was fast, yet my K20D and DA*50-135 managed to nail it.
I've also shot my daughter at an indoor skating rink with the K20D and DA*16-50, and had little trouble locking focus, even though it was so dark I couldn't even read under that light.
Now, would another brand focus faster? I don't know, but I guess so. I
do know that the K20D is fast enough for me.