You'll note that the ability to activate/deactivate OpenGL isn't in the CS6 preferences any longer. Nor is it in the Comp viewer settings.
My understanding is that the new Fast Draft is OpenGL always on. You may need to adjust your Fast Preview Preferences and lower the Adaptive Resoulution limit.
Brian Maffitt has a tutorial on the new performance settings here:
http://tv.adobe.com/watch/learn-after-effects-cs6/enhanced-performance/
I've had such a positive experience so far with CS6 on my MacPro, though I have the 2010 model and a different video card.