For wow is hard not having issues with FPS. In my system i play ultra 1600x900 and flying around in most zones i get more than 100 fps (GPU usage 100%), while in a battleground or LFR 25man i get 20-40fps (GPU usage 40-60%). Even in ogrimmar, when its really populated i get 20fps near the bank(GPU usage 15-30%). So the problem is the game, not the hardware...
Overclocking it will help a lot, becasue wow likes faster frequencies. But you should understand and accept as many of us that WoW is another bad optimized game
Mostly becasue it still uses the same engine from 2004 when it was launch.
Best regards, sir