Originally posted by pingflood AF on par with a 50D? I'd love for that to be the case, but I very seriously doubt it. The 50D is blisteringly fast and dead accurate in AF-C mode when tracking.
The 40D and 50D have the same af system in general, their afc is shutter priority ( af syncro or servo or something ), ie doesn't wait for focus. Also note that one needs to test similar speed lenses, ie NOT the 50-135 as it is slow to af vs the 70-200 usm but lets say give both a sigma 70-200 hsm lens and then try it, the K7 will surprise you! I didn't do bench mark tests but did compare in real world, the K7 is on par imho ie will get similar results, it has caught up to the point that a user will not immediately notice a difference between the 2. The D300's af I do consider better than either with the 70-200vr f.28 from what I have seen. Do note that the environment I have used them in is very uncontrolled and just apparent af speeds time to lock etc.
Case in point, during carnival here when I first was using the 50-135 AFC was near useless on the k20d and I was getting to many oof shots, switching to the 70mm and 40mm the faster af helped alot, to the point I was holding my own with out needing to switch to the d300. Another photog with a 40d and 5d next to me was suddenly surprised by the pentax, his lenses were not the canon usm but sigma and tamrons that did not af as fast. The lenses af speed plays alot into it and too many tests do not level the playing field, Pentax does need faster af IN THE LENSES but even then with the 50-135 on the K7 it can track to a level it won't be embarrassed by a 40/50d or d90. Hence again, on par.