There is a nice overview for compatibility and state of implementation:
http://www.x.org/wiki/RadeonFeature
I'm using a 5850, but it seems the support for mine and your card is almost the same.
I just switched from the proprietary to the opensource radeon driver, which WORKS SO MUCH BETTER in terms of 2D Desktop.
I have a flicker-free desktop at last, no tearing when watching videos.
With the proprietary ati drivers, this was only possible with "tear-free desktop" activated, which caused a really laggy desktop.