It’s also important to consider the two possible (and not necessarily conflicting) reasons why larger displays are desirable:
– To show more content on the display at once.
– To make the content on the display physically larger. – Daring Fireball

Gruber posted an in-depth overview of all possible and impossible resolutions for the new iPhone 6. Instead of just posting the numbers, he breaks down every option and clearly explains why that specific resolution is or isn’t a good solution.
Take your time to read this one, it’s dense.