http://bugs.winehq.org/show_bug.cgi?id=15925
--- Comment #43 from Jerome Leclanche adys.wh@gmail.com 2009-06-12 00:09:45 --- Update on this bug.
The performance drop is minimal, now. This may be improvements in Wine, or Blizzard improving their engine, or more likely both. Disabling or enabling vertex shader/pixel shader no longer has any visible impact on the game's performance.
Both in D3D and OpenGL modes, WoW has improved a LOT recently. Running the 180-185.x nvidia driver branch also helps, which may mean the nvidia driver had some bugs as well.
I think it's safe to close this bug as fixed.