I could handle something bigger than my 4.3 inch Archos which I use as a small tablet.
My Kindle is 6 inches and even if I take away the keyboard and big bezel, it would be too large for my pocket.
So the question in my mind is how much larger than a 5 incher would be practical to carry?
This of course assumes a small bezel and of course some compromise on aspect ratio.
Frankly, I kind of like these kinds of choices.
My bet is on a 5 incher being the most acceptable for the majority of users.