I am running with a 970, but everything is fine, mid 90's for FPS. I am using the latest web drivers and I also have the latest CUDA drivers installed. WoW is also up to date and on new xpac.
I had an issue with black screen when I started WoW right after I got my computer up and running, I had to delete and re-download and everything worked fine, I reckon there was some hiccup in the download and a bad file (I tried repair client as well, but it never showed anything).
If you have the time and a good internet connection I'd suggest re-downloading the game client and see if that helps at all.
The Mac side of WoW is a bit in shambles at the moment as previously mentioned, I was reading a bunch on the forums and it seems there is a SERIOUS lack of Mac dedicated employee's at blizz (I want to say I remember reading there was only 1 person qualified to work on the mac client... ridiculous!).
HOWEVER, if its working fine for myself and others there is no reason it shouldn't for you.