I'm using Premiere CS6 with OS X Mavericks on an two monitor machine. With OS X 10.8. I have no problem with using the second monitor as a full screen video ouptut activated under: settings / playback / videodevice (translated from the german version)
Now with OS X Mavericks the display output from the second screen is overlayed on the first screen which is useless.
.....just find the answer. You have to untick the option in the OS X system settings under Mission Control "Display using different Spaces" (Monitor verwenden verschiedene Spaces)