Quote: K10: zzzzzzzzzzzzzzzzzzzzzzzzzzz-z-z-z-z-z-z-BEEP
K7: zzzzzzzzzzz-z-z-z-z-z-z-BEEP
D300s: zzzzzz-BEEP
As far as quietness goes...
If you want quiet, consider first disabling that annoying beep... There's a green spot in the viewfinder which confirms focus :P
For my part, every single time I have heard someone complain about camera features, it has been a case of user knowledge or experience. Let's be honest, people shot sports with MF lenses. I still do. I can shoot sports (and did, often) with compact P&S. Knowing your equipment, how it works, its limits and possibilities will get you a long way. The Nikon might very well be faster, I've never used it. but there's never been a case in my two years with the K20D when I could honestly look at my camera and say "frigging gizmo, YOU are slowing me down"... It's always been the reverse.
I will also say that, apart from the 50 and 70, the lenses listed are not the best choices for sports. A faster lens will give more light to the AF sensor, and increase the speed. Consumer lenses will not deliver miracles.
changing systems is always done with a huge loss, so as for me, before changing I'd consider practicing and learning.
(for the record, there ARE things certain cameras can and can't do. built-in SR, servo-AF, are actual features that might be there or not. But we're not talking about this here).