Xcode 5.1.1 together with xCode 6.1.1 - simulators deleted
You don't need both versions of Xcode in order to test with iOS7 and 8 simulators. With the latest version you will be able to test in both simulators. You just need to go to Preferences → Downloads and download the iOS 7.1 Simulator. Then you can define simulators with that version on your devices window.