Is it a network issue or is the CPU the bottleneck? Can you run activity monitor while mirroring and let us know what it reports in terms of CPU usage?
Airplay Mirror works rather well on iOS so I'm hopping it'll perform decently on OS X.
AirPlay works well on ios if it's video material like mov or YouTube or a video stream, but if you just share the screen as open up a game that doesn't have inbuilt air play, it lags to death as well, totally unusable.
They surely don't. I took a moment to test today on a macbook pro retina display and Diablo 3 was amazingly fast via AirPlay. There was no lag and I was playing at the highest resolution. The frame was taking my whole TV (no black bar on any side). Truly amazing I have to say.