Check out the iOS Design Guide for iPhone 6 and iPhone 6 Plus I have written for 2020apps.
This guide includes common UI element and common app icon sizes for iPhone 6 (@2x) and iPhone 6 Plus (@3x). It describes the how the larger 5.5" screen handles the downscaling to 1920x1080.
It answers all your questions about designing for Apple new devices!
If you have any questions you can shoot as an email to hello [at] 2020apps.io
Happy designing dribbble friends! :)
iOS Design Guide for iPhone 6 and iPhone 6 Plus. [PDF]
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