but a lot of that is CPU related.
Simplexity88 brought up a point that I failed to mention, WoW is still very dependent on your CPU. Look at it this way, questing, farming & 5 mans are handled by the GPU. Once you get into the 10 mans, 25 mans or major cities during peak times, that's when your CPU starts to show it's true grit, so to speak.
The 7750 is plenty capable of handling WoW at High maybe even Ultra but also take a look at your CPU, which you didn't tell us.