I think phones over 5" are too big for a phone,
I have an HTC One M7, it's pretty much perfect, fits in my pocket, and can be used with 1 hand easily.
My biggest complaint with the S5 is it is too big for single handed operation, not that it can't be done, but I have a buddy that's gone through 2 screens on his S5, drops it often due to the size. With the case he says it's near impossible to text one handed
Keeping the sides tight to the screen is important for a larger phone. Like the Lenovo pictured in the post above, if a company goes big screen, they should keep it a tight as possible width wise
For me personally phones need to be small enough for single handed operation, I like the 4.7" screen. Tablets have use, I love my 8" galaxy tab, after that I go laptop, then desktop for heavy use. 10" tablets are an awkward size IMO, too big yet too small.
I want a 14-15" tablet with a full windows version to replace my laptop
Sony 75" X940D, 7.1 Klipsch, Onkyo TX-NR656, Xbox One/360, Nvidia Shield Alienware Alpha, Arris Gateway, 42" Samsung