Well, here is my .02. Under video, quality, video quality, uncheck "enforce smooth video playback". This will allow you to change the other settings. Uncheck all of the adjustments, especially dynamic contrast (which is probably causing the flicker) Depending on what you watch, you may want to experiment with some of the settings. If you primarily watch HD and blu ray, I think it is best to turn them all off. Uncheck automatic deinterlacing and move the slider to "vector adaptive". Check pulldown detection.
Go to video, color, and select "use player settings" and scroll down to the dynamic range setting. Use whichever looks best on your set. Apply the settings. Be ready to go to watch something one day and see some of these settings have changed. In my experience these settings don't always stick, one of the quirks with an ATI card.