I now can confirm with the updated drivers for the nvidia card (GT120+GTX480) that PProCS6 works perfectly smooth even with a lot of MagicBulletLook use (h246 and ProRes clips / 1080p25)
here are some links you might want to check:
QUADRO & GEFORCE MAC OS X DRIVER RELEASE for 10.8.2
http://www.nvidia.com/object/macosx-304.00.05f02-driver.html
current CUDA for 10.8.2:
http://www.nvidia.com/object/cuda-mac-driver.html
Optimize rendering settings:
http://film-sound-color.tumblr.com/post/31268656116/if-u-have-issues-exporting-or-even-rendering-stuff
GPU for Resolve9 AND PremierePro CS6 in ONE system:
http://liftgammagain.com/forum/index.php?threads/gpu-for-resolve9-and-premierepro-cs6-in-one-system.580/
How To Enable GPU Cuda in Adobe CS6 for Mac:
http://film-sound-color.tumblr.com/post/26071716910/how-to-enable-gpu-cuda-in-adobe-cs6-for-mac-by