@Aubrey:
I use SD on an iPhone 6 plus and I feel it's an excellent screen size.
Can you share a bit more? Does the always enabled mobile net causes trouble with interference with radio or audio panel? Is SD scaled to use the pixel of the 6 plus already? Maybe you even have a picture of it mounted in the cockpit? I am into replacing my iPhone5 pretty soon and was thinking of using the 6plus, getting off my RAM mounted iPad Mini as well.