No one has a steady framerate in WoW. I play with vsync enabled so its capped at 85 @ 1600x1200. This is the performance difference in different areas.
Barrens or Badlands: 85fps
small towns (like brill or goldshire): 70fps
Orgrimmar or IF: 30fps
Grom'gol area: 17fps
This is just some of the performance numbers I remember. What im trying to say is that you cant state an average fps for WoW because it varies so much by your location.
I play at 1600x1200 w/ 4xAA and 16xAF because im totally CPU limited up till that.