Do you have any 3rd party add-ins installed? These can have a very detrimental effect on fps.
I've always found wow to be fairly poorly optimised, especially in comparison to games that are far more impressive graphically. Also, fps always seem to drop after an expansion. Fromw
Hat I gather, wow is more cpu intensive than gpu. Do your frames rates improve if you lower resolution? (that will help identify if it's cpu or gpu limited).
You could try taking off the frame rate limiter (something like set maxfps = 200), look it up on Google.
What issues are you having with bc2?
If it's across the board, could be faulty gpu, but if you're fine on b3,then I'd be fairly surprised.