Noticed this thread on the Rage3D Linux (ATI) Drivers forums:
Fix for WoW in OpenGL mode in wine/cedega ( http://www.rage3d.com/board/showthread.php?t=33807135 ).
Basically, it seems to involve hex-editing WoW.exe (!!!) to filter out a couple of extensions (mainly GL_ARB_vertex_buffer_object), which sounds rather horrifying, but does apparently result in vastly improved performance in OpenGL mode for ATI users under Wine and Cedega.
Now, I don't play WoW, I'm no programmer, and this may well be an ATI-specific issue, but maybe the hack listed here will shed further light on the DX9/WoW work currently needed/being done.
Just in case it's useful info that no one happened to see :) . If not, please ignore and apologies for the interruption.
Holly