WoW on Base 27" iMac

Welcome. Are you talking about the most recent base iMac models?

 

I have the new 27 i5 and the game runs very nicely with all settings on high!
frame rate mostly at a consistent 60fps but will drop in areas with loads of ground clutter such as plants etc... You can always turn ground clutter down if this bothers you though. Vsync is a must or you'll be seeing massive tears.
Overall the 27 i5 runs the gave very well and so it should considering the graphical demand of WoW is pretty low. Hope this helps and just ask if you want to know more.

 

Some ppl said the Lich King areas may give it some trouble or something like that.

Note that if you're planning on Cataclysm, they are revamping the world and going DX11 with some demanding special effects. There are some beta videos on youtube if you don't mind spoilers that talk about it. I don't know how this will affect the latest OpenGL or whatever though but if they also add "effects"...