I have dual GTX 580 and I can run at ultra setting but I still get occasional slowdown during heavy boss encounter at max setting.
I use Logitech G15 to show many things and when I set to display the CPU and GPU usage, 2 CPU cores are maxed but maybe 10% of GPU is being used for WoW.
Keep in mind that WoW is based on 8 year old spaghetti code that were originally optimized to run on CPU more than GPU. Back then, some of the top GPU were a mere 256MB 128bit on AGP slot. The core code has not been fully redone to take advantage of modern technology, which is why WoW never takes full advantage of your newest top of the line $1,000 video cards. Other games that are coded recently will work far better with superior GPU and decent CPU. WoW still works better on superior (and especially well overclocked) CPU and a 4 year old video card.
Quoting for truth so OP can ignore the other arguments about 'lol this game has graphics so y u talk about cpu lol'.
@OP, my current graphics card puts up benchmark results that are less than 10% higher than the one you posted and I run everything on full ultra just fine. But as stated, if your CPU is garbage the best GPU in the world can only do so much.