However, according to a new investors note, there may be another crucial difference between the screens on these two phones other than their size.
The larger 5.5-inch iPhone is likely to come with a sapphire display, while only certain versions of the 4.7-inch phone will feature a screen made of sapphire, according to analyst and investor Matt Margolis (via 9to5Mac).
Margolis is an investor in GT Advanced Technologies, the sapphire plant Apple inked a deal with last year in November.
Margolis cites sources to Foxconn's manufacturing operations, saying that some 4.7-inch models will use sapphire covers while others will come with Corning Gorilla Glass, which Apple currently uses for its smartphone's screens.
This corroborates with a report from The Wall Street Journal earlier this month that suggested only certain models of the iPhone 6 will come with a sapphire screen. It's unclear if this means models with sapphire-coated screens will be priced differently, but since sapphire is expensive to produce in large quantities, it certainly seems plausible.
Sapphire is ideal for smartphone screens since it's considered to be extremely durable and scratch resistant. YouTube tech personality Marques Brownlee posted a video reportedly showing the iPhone 6's display being scraped with a knife and bent underneath his shoe without a scratch.
We expect to learn more on Sept. 9 at Apple's event, where it will presumably unveil the iPhone 6 and possibly the iWatch.
Other than a larger scratch-resistent screen, the iPhone 6 is expected to come with a slimmer design and a special chip dedicated to measuring your health stats, among other features.