Re: Image tearing/image artifacts during video playback
Did the situation improve when you
a) Turned of a compositing manager, but kept the X composite extension enabled
b) Disable the X composite extension
From your description, it sounds like you did (a), but you need to do (b) to get tear-free video at present. This will be resolved soon.
If you did in fact do (b), please see the driver README for a description of cases where overlay v.s. blit is used. Something is still forcing you into the blit path, if you are still getting tearing.