Yes, there is a way to simulate the metrics in Storyboards.
In Xcode 5:
Once you open your storyboard, if you look in the bottom right corner, there are a set of buttons. The single button on the left will toggle between the two iPhone screen sizes, so you will be able to to make sure that your app looks good on both screens:
In Xcode 6:
Simply select the ViewController you wish to simulate by clicking on the top tab (with the three icons), select the Attributes inspector and specify your size under Simulated Metrics -> Size:
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