I wouldnt recommend a 5830 to my worst enemy, its just not worth it. If you want to see a big jump in performance get a 5850 or greater. The 5830's are crippled 5850's with a crazy price-tag. If you can get one for under 200.00$ then I say go ahead, if not get a 5850.
For WoW I would stick with what you have, buying a new GPU for that specific game is not worth it. If you were getting 50 frames or lower then a new GPU would be a great upgrade, for now you are fine. Do you play any other games besides WoW?