If your building a new PC to specifically play WoW on then your primary focus should be your Cpu and overclocking it as high as you possibly can. With the new Nvidia "wonder driver" that came out last week we gained easily 10-15+ fps since it reduced cpu overhead and moved some of the reasources to the graphic card but even with that WoW is a old as shit Cpu bound game. The difference between a stock Intel i5-4670 @ 3.5 ghz (guessing on that speed at stock) and one at 4.5 ghz is night and day. You could buy a titan black or even 2 titan blacks in sli and not receive the same fps increase you would from getting a good OC on your cpu and having a good aftermarket cooler. I would absolutely get a K variant quadcore and the Noctuah d-14, read up on some overclocking guides here on tom's and go to town. If your budget is tight lower the gpu to a gtx 770 and save yourself $200 and put it into those 2 items i just mentioned.
Im running a 4930k @ 4.7 ghz with a gtx 770 and a noctuah and loving life in WoW, 100+ fps in open world 50+ in the middle of Org on Tichondrius at a peak time. My build was all individual upgrades over time, and I also OC'd way after I bought my Cpu and it was by the far the greatest increase in fps.