Even 5.5in may well seem pathetically small by September. I bet Samsung are already working on 6in+ phones. Its a screen-size arms race and Tim Cook knows that Apple need to catch up!
In fact, analysts predict that by 2016, ~80% of smartphone screens will possibly be bigger than the iPad is today.
There are already a number of 6+ inch phones on the market, I have one. I don't think the market will move up that far. It's so big that I have hard time sitting down with the phone in my pocket.