ATI Displays Control panel.

[samsc]

The ATI displays Control panel seems to need to be installed on recent OS builds to get the best performance out of Catalyst and Pixelmad

http://www.versiontracker.com/dyn/moreinfo/macosx/21573

Users of these applications running their displays at 60 HZ might have noticed some performance problems.
And at 75HZ users might have noticed some frame tearing.

These issues seem to go away if the ATI display control panel is installed, and set to run in the configuration shown here.