I don't think it's the gpu, as everything else looks fine, no artifacts. Maybe there is a partially corrupted file in wow that causes this. Have you model edit or install addons from unknown sources? Also, did you have a virus attack recently? Some viruses can mess up with your installation.
1)If non of the above, uninstall wow completely, delete any remaining files, uninstall any programs like Curse client, restart PC and redownload the game from battle.net.
2)I would also recommend updating your video drivers and uninstall programs that come from unknown / untrusted places + a virus scan.
Try 1) first and see how it goes.
ps: Generally, you should post such problems on the blizz official forum. They know best when the problem is technical.
No idea what that links to but probably less safe than www.nvidia.com or www.ati.com . It looks like a video driver problem. If that doesn't fix it, clear the cache out, but I'd say it was more likely to be driver.