I am in the exact same situation, except that I opted for Nexus 4
Was very disappointed with iPhone 5. Don't get me wrong, it's a good design, thin and light, but looks a little awkward being so tall and actually feels like some sort of knock off in your hand. I have in the past always protected the screen size of iPhones, but having used my Nexus 4 for just over 3 months, I must admit, the 4'7" screen is amazing (although if it were just slightly smaller, I could you use one handed for most tasks. maybe 4'5?). iPhone looks weird after N4
So, I would welcome a bigger screen size in iPhones, but 5" is probably a little too big.
But I personally think, that apple should concentrate on the iOS rather than hardware. I haven't used Android for almost 2 years until N4 and google have done a great job. The whole argument about iOS being smoother is hardly an argument any more, as the gap is too close, but otherwise android seems to be way ahead.