I would also agree that the sweet spot is somewhere between 4.7-5". I've had no problems using my 4.7" Nexus 4 with one hand. Typing with one hand can be tricky but possible, although I prefer to thumb type with both hands. Anything beyond 5" is where diminishing returns start to show. Any larger, such as a 7" phone Asus Fonepad would be laughable. I've used it as a tablet and its just too large to fit in anyone's pocket.