The i6 isn't much of an upgrade at all on the 5S actually. You're really only getting a bigger screen and an uglier phone. Most iPhone owners were perfectly happy with a smaller screen, right? Otherwise they wouldn't have bought the 5S. So why is a bigger screen now an 'upgrade'? The rest of the spec will make zero difference in real world usage.
Now that I'm ready to move to a bigger, better screen it seems like quite an upgrade, tbh. I mean there are tons of Android fans who openly say that they switched to Android because of the bigger screens and nobody has really questioned that until now.
Plus the better camera and processor and NFC (if they bring it to Canada) are cool, and I can leave my jailbreak on my 5S and enjoy iOS 8 on my new phone.
Beyond that, I just didn't want a 5.5 phone. I've looked at the dimensions and if I'm already uncomfortable with things like the Note, etc, why would I want a phone that's even bigger, with huge bezels?! I wouldn't.