Hey guys, I play WOW and D3 quite a bit on a 15" rMBP using a 24" as a primary display and extended desktop over to the retina display. I watch netflix on the secondary display while gaming. After installing Mavericks, my game fps in WOW dropped from 70-80fps to 17-20fps. I played with settings, turned off energy savings to see if the discreet card wasn't getting used, changed wow settings and was really racking my brain trying to figure out the heck happened. As it turns out (and we've seen in other threads on MacRumors) in 10.9 there is a new feature for external displays that has the menu bar appear at the top of the second display. This feature is in Mission Control called "Displays have separate spaces" and is turned on by default at install. To resolve the low fps, simply uncheck this in Mission Control. You will loose the menu bar on the secondary display but gaming fps will return to normal. There is something about running video in a separate space (as opposed to the same space but extended) that kills the system. Just wanted to share in case you guys are looking for an answer as I hadn't seen anyone encounter this yet!