I think something that's often overlooked is that there are two distinct groups of phone users, or in this case Note II users. Those who generally use phones with one hand and those who use them with two hands. I've always handled most tasks (at least 90% not including phone calls) with both hands and this was even true with my previous phones (Evo 4G & E4GT). For people like myself, moving to the Note II was very easy and the potential of the stylus only helped to make it easier.
Anyway, I think I could go bigger and while 6" may be viable in terms of usability, I'm honestly not sure if I'd want a display quite that big. That being said, I can't see anyone who uses the Note II predominantly with one hand wanting anything bigger.