Originally posted by kunik odd since k20d does not have predictive AF.
K-7 does though.
Actually, they both do, to the extent that it allows for time-lag before the shutter opens. However, with fewer reference points, its much less effective at close quarters, low contrast or random movement.
However I generally have no issues with motorsport, air-shows or other similar events provided the light is good and the background is not too busy. For bird or wildlife photography its not good at separating subject and background, and doesnt help you maintain focus on a small object when panning like a multipoint system does.
Is the Nikon D300 better in more cases, yes of course. However in some situations the Pentax system is entirely adequate such that it may even come down to the lens used. My K7 is certainly a major improvement over my K20 in that it takes a lot more smaller increments when focusing continuously (even if you dont press the shutter).
Incidentally, having used the 70-200 F2.8VR on a D2X I cant say its all that fast. Both Canon versions are faster, especially the 70-200 F4 which is really quick.