http://cdn0.techbang.com.tw/posts/5124-8-interchangeable-lens-camera-auto-focus-video-big-pk
(in Chinese, Google English Translation Here)
The first test and video set shows the (different) speeds of the cameras in continuous AF mode during video recording. Note that not all the cameras have this mode, e.g., the Canon 600D and 550D do not have this. The second test and video set shows the speeds of different cameras in single AF mode (manually executed) during video recording. In this test, I have to say the performance of the Canon 600D/550D is the worst - the AF speed is slow and serious hunting can be seen.
Btw, Pentax DSLRs by no means could participate in this test as no Pentax DSLR ever made could re-focus in AF once video recording is started! :-(
It is pretty sad that despite now the LiveView CDAF of the current Pentax DSLRs (i.e., the K-5 and K-r) are already faster and smoother than the CDAF of the current Canons, Pentax still has not made the AF possible during video recording! On the other hand, I am rather disappointed to see no improvement at all for the 600D over the 550D in this department. As for Pentax, I just wonder, how is it so difficult to implement also the CDAF *during* video recording? Even if there is no option of the C-AF, why not at least a single AF on demand? :-o (Which would be fast enough if Pentax did it! BUT only "IF and Only If"!!)