Well sat here playing with the 6 and 6 Pro together and I've gotta say, I prefer the Pro. The size difference is negligible, about 5mm taller, and 1mm wider. But the Pro feels better in the hand ('Ladies' /Flossy Carter)
The zoom on the camera on the 6 is a step down from my 4XL with its 2x zoom. The telephoto on the Pro is brilliant.
Don't mind the curved sides.
They are both like bars of soap!
Screen looks better on the Pro.
Not a fan of the FPS but I never was, my fingers just don't get on with them, I already miss face unlock (and motion sense!)
Is it worth the £250 more? Dunno, that's up to the individual, YMMV. Will play about more later.