unless their next 5.5 iPhone gets actual FEATURES that take advantage of a bigger screen i dont see the reason to use anything more than 4.7 tbh. i am already annoyed that my iPhone 6 is bigger than my old nexus 4 with the same screen size. could have fit a 5.0 screen in there almost
iPhone 6+ has (software) features that the iPhone 6 has not - many apps (including Apples) make use of the bigger screen in ways that are not available on the iPhone 6. Also the better battery is a big plus.
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I have an iPad mini too, for when I want a larger screen... laying on a couch.
I (and millions of others) also want a decent sized screen on a device that we can pocket.
That's because the "phone" we carry is not just a phone. It's "an iPod, a Phone, and an Internet Communicator", as Jobs said. (Jobs refused at first to call it a mobile computer, but that's also what it is, perhaps even more than the others at times.)
My iPad mini is mostly unused since I have the 6+ ... didn't expect it first, but it the 6+ screen is big enough for me (but thats me, others might see it different) - it is just the few 'iPad only' apps that make me pick it up from time to time (hope they get a 6+ port soon)