After a recent question of mine (https://apple.stackexchange.com/q/116029/7742), here is some info:
My app was developed using Xcode 5, iOS SDK 7. Deployment target is 4.3.
I was told that the 4th generation iPod touch can't run iOS 7.
Since my app has a deployment target of 4.3, then it should run on that iPod, right? Or does the fact that I used the SDK 7 mean that it won't work?
iPod Touch, 4th Gen DOES NOT support iOS 7. See this Wikipedia article.
You CAN use Xcode 5 to build an App with a deployment target of 4.3, but that means you CANNOT use any iOS feature supported only by versions of iOS > 4.3. And you will have to be VERY CAREFUL to check that you don't, or the App WILL crash.
And... unfortunately there is no Profiler or Pre-Processor that warns... although you can double check if Xcode "Analyze" warns you. Else you just have to very carefully check all your code for conformity with the limitations of the 4.3 SDK or test a lot... well actually do both.