I'm having the same problem on Windows 7. Are you suggesting the same solution on Windows?
That is -- uninstalling all 17 or more Master collection programs and re-installing them?
I had much better performance with CS5.
Now in addition to the dismal preview rendering (which was great in CS5) I'm even getting weird bright color screens instead of the image on video sequences where I've overlaid images with transparency over them.
Thanks for any help!