It depends on your budget, you can build a second machine to run 5 more wows "decently" for about $500 and run 2 machines, 5 on each. Or you can build a machine for 800-1000 to run all 10 on failry smoothly. With the lower costs of everything lately I definately would go with a quad core, most likely amd as they are best for price to performance ratio. Somewhere on here someone had a post about running 20 WoWs on a single AMD quad core phenom 3.0 with like 24 gigs of ram lol.