We think of it as lens motor speed but it's more than that. The K-3 already has faster AF than a Nikon D7100, and probably most other APS-c cameras. I'm thinking the AF system in the faster Canons and Nikon are probably worth more than a K-3 given the cost of those systems. The question is, if they speed up the lens. will the camera start to miss focus. Just from my experience with my Sigma 70-300 on a K-3, I can say at ƒ6.3, that lens will miss focus. It goes right by the point in focus without a blink, sometimes I have to focus manually then use AF. I suspect, faster focusing AF would be great for 2.8 lenses or faster, but would be a nightmare for slower lenses. Now we are running into the small camera company thing. Canon and Nikon can beef up their AF systems to handle this kind of stress. Pentax really isn't in a position to come out with a $3000 AF system on a $6000 camera. If everyone of us who should buy it did, they still wouldn't have enough sales to justify the investment. They pretty much have to try and excel in other areas.
So long story short... faster AF is only an option on fast lenses with expensive AF systems. I doubt faster AF will even function on slower lenses. And faster glass on a K-3 will probably already be excellent on a K-3, which has one of the most light sensitive AF systems out there.
But just to agree with your point, there's no excuse for SDM lenses being as slow as they are. The AF system can handle more speed. The star lenses should be able to take advantage of that. Especially since the Sigma 70-200, the only lens that really did take advantage, is no longer produced in a Pentax mount.
Last edited by normhead; 12-04-2014 at 08:44 AM.