In order to test something for another AppGameKit user, I allowed my iPad to update to iOS 6.
Then it was not recognized by Xcode 4.
Then I got offered the Xcode update and installed it. It took an hour for it to download. After installation, it no longer allowed the selection of iOS 5.1 SDK. And a built app will not run on my iOS 5.1 device.
I finally discovered how to be able to build and test for both, at least in theory.
Use Xcode->Preferences->Downloads to add the iOS 5.1 Simulator. This lets you use the iPad/iPhone simulators for both iOS 5.1 and iOS 6. You can install other simulators as well.
It also let me build/install for my iOS 5.1 iPod Touch. To build/run for iOS 5.1, set the iOS Deployment Target to 5.1 in the Info panel for the project (not the target info panel).
However, I'm having difficulty getting my previously working app to install on my iOS 6 iPad. Further testing/investigation needed.
AGK Community Tester