I'm very conflicted on which one to choose.
My first instinct is that the 5.5 is too big for a phone and my pocket. Will it really comfortably fit in my pocket? Also, will I be embarrassed to use it in some situations? It wouldn't be very discreet using such a large device for a quick second.
On the opposite side of that, Apple seems to be positioning the 5.5 as their gem, top of the line. That makes me want it.
Furthermore, my old grandfathered unlimited data would be pretty nice on the 5.5. A 5.5 device would be pretty good for consuming and some creating when away from home, with unlimited data.
The 4.7 will feel like a slightly upgraded iPhone. It would be better, but probably feel more like a bump. It would serve great as a phone, but is it enough of a jump when the 5.5 will offer much more? After all, these carrier upgrades don't happen too often! Time for me to decide!