Just a few quick notes. Looking at and playing with the latest beta for 10.6.5, the problem doesn't seem to be fixed.

There does however seem to be a possible fix coming in 10.6.6 but that is probably still several months away.

If you are using Phoenix to do video capture then stick to 10.5.8. If you are not doing Capture, you can use 10.6.2 with the QT update.

If you need Catalyst machines right now, I suggest purchasing used machines. Late 2006 machines with x1900, Early 2008 machines with 8800s are my two top choices. Early 2009 machines are decent also but the 4870 requires the mdp-dvi adaptor I'm not to happy about.

A good rule of thumb is to stick wit what works and is proven instead of trying to jump to "more powerful and newer"