your pc should run 5 with all the settings low, i'de stay away from major cities though, you will lag alot, WoW is more ram dependant than anything i find, and i dunno too much about anything but Nvidia cards, but the rest looks good enough to sneak by with a 5 box team, but you are pushing the envelope :P

easiest way to know for sure what your pc will handle is make 5 trial accounts and set it up and run around and see what it can handle.