The iPhone 6 will be 4.7 inches. That said, I just got a 5.5 inch Android phone (I love the iPhone but need a big screen due to vision issues) and my iPad is still just as useful as it was before. Here is a pic of my LG G3 (5.5 inch screen) and my iPad Air.
Reinforces for me that the 5.5" iPhone 6 and an updated iPad (Air 2 I reckon) is just perfect for me.
It would really take something to move my off my iPad. It was good enough to move me from my desktop PC (and my other half from her laptop 95% of the time!)