You're thinking is taking you in the right direction. GT 555M or Radeon HD 6770M.
You probably won't find a i7 CPU in your price range but a i3/i5 CPU should fit into the budget. BF3 at low graphics settings, WoW/LoL at high. Lenovo IdeaPad Y570 15.6-inch "Sandy Bridge" Laptop $669
Core i3-2330M 2.2Ghz CPU, 4 GB RAM, 500GB HDD 15.6" 1366x768 LCD w/ GT 555M graphics.