Before updating to 10.8.3 and the new CUDA driver, I had some choppy playback problem with my config:
GT120 and GTX570 export was fine but not real time playback.
Now with the update, I get full playback with that kind of nodes (just for testing):

out of my C300 file
which was never possible even with 2 or 3 simple node stuff before.
Greetings
Philippe