Study shows ? With what demographics ? If a study is done for neanderthals it'll surely show that 10.1 would be ideal. C'mon gsmarena. You're not a newspaper that you have to fill up columns. It's all relative to palm size as someone has said already and that's why women prefer it smaller in this case :) and I concur that 4" is big enough already if you're holding it against your face and for upclose viewing purposes. Better screen res is what is important along with daylight readability rather than a bigger screen.
i think 4.3" is the perfect.good for net-surfing but fits in the denim or formal trouser as well. it will be handy too then.
though i am using a phone with smaller screen, my next phone will be with 4.3" with quad core processor hopefully.
4-4.5 is perfect for me I have big fingers and hands. I had iphone 3GS but 3.5 inch is too small for me. I hope next iphone will be 4-4.3 inch.
4 - 4.5 are for giant hands..size should be 3.5 to 3.7 just....fit in pockets
My dell streak 5" still fits in my pocket (no skinny jeans here), and the screen is big enough to be useful.
3.2 inch to 3.7 inch. Larger screen size is helpful for only those having large hands and large palm.
galaxy note 5,3 inch is perfect, for my hands, cell phones screens 4 everywhere