My PC (which is a little less powerful than the one you have described) run World of Warcraft on Graphics 10 in raids with more than twenty players no problem.
I just bought a computer with an i7 6700 CPU with a GTX 1060 graphic card and 16 GB of memory with the hope I could run WoW on ultra (best I've ever really had was medium). Now I'm apprehensive that I could. I haven't gotten the computer yet and likely won't for another two weeks since it's still being built. Figured since the computer is well above recommended specs, it should run WoW fine on ultra. Guess not. But if everyone with a higher end system is being recommended a 7, wonder if Blizzard will fix that with the first patch to give true recommendations.
Pfft, silly Skylakes. Everyone knows best CPU for WoW is the i7-4790K... It recommends 10 with one of those.
i5 6600k, 980 TI, 16gb of memory, and it recommends me 7 as well. Everything is fine and dandy at 10 however but your mileage may vary of course.