A bigger iPhone may not be better, but it makes sense for Apple
Wired - 08/08/2014
But while UX is one issue, larger phones are more difficult to use from an ergonomic standpoint. Northeastern University professor of physical therapy Jack Dennerlein said a larger handset “means more awkward postures of the thumb, and reduced performance when using it with a single hand. As the size gets bigger too, the devices are harder to hold: Optimal grip is usually around 2.5 inches.” Larger than that (the current iPhone 5s measures in at 2.31 inches wide), and you could actually put yourself at greater risk for of a repetitive stress injury.