Got my hands on two iPhone 6 cases. Took a bunch of pictures comparing them to the iPhone 5S, Nexus 5 and Sony Xperia Z2. It's almost identical to the Nexus 5 size, which I think is perfect and not too big/small. My thumb can still reach around the entire screen without requiring two hands to hold the phone.
See full photoset here.
Sample photos:
See full photoset here.
Sample photos:

