1. Don't buy a prebuilt one. You get so much more satisfaction from making one yourself. Its really not that hard; I had no knowledge of computers before I made mine, and now my plan is to go and study it in college.
2. Stay away from the AMD FX-processors, as they are nice, but WoW I believe is more of a CPU intensive game, so something like an Intel Core i5-2400 or 2500. They are not good value either.
3. You can make something so much cheaper that will play LoL at 60fps its rather insane.
How is something with that specs $919?