The phone is only 8% larger than the existing iPhone 5S, this increase is to accommodate the larger screen.
Sapphire Crystal display
The use of sapphire crystal as opposed to Corning Gorilla Glass has been widely rumoured in the past 6 months. The benefits of using Sapphire Crystal come mainly in the form of added strength/durability and added scratch/fracture resistance.
The next iPhone is widely expected to sport a larger, higher resolution screen. This is an area of great contention as changing the resolution can cause major problems for developers to update their apps efficiently.
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The digicam sensor could be up to date, possibly to a 10-megapixel sensor and an elevated aperture of f/1.8. Different capabilities expected are a faster and more green A8 chip.