I gave it a try but wasn't impressed by the performance. My FPS was about 4-8 lower than Windows version. With the Mac client I noticed that start up, map loading, and texture loading was slower. When walking around the FPS would drop a lot and everything would become very choppy. The client also has a lot of bugs that are mentioned on GW2 forums.
I took a comparison screenshot and matched the settings. Texture setting will only go to Medium and others are disabled on Mac client.
The Mac client is a transgaming cider port so I'm not expecting windows like performance but, Anet has a lot of work optimizing it though.
Web Designer & Developer @ Tinyminute.com / Gamer / Apple Geek / I.T. Guy / MacBook Pro User