I have the Developer edition of the older 13 - its a 13" display in closer to an 11" form. The 13" and 15" have really tiny bezels to hit their dimensions, with the new 15.6" being 14" wide.

The 13" developer edition was close enough to perfect for me with the 1920x1080 display, battery life takes a hit with the 4k screens. Getting a 15" this time around, but expect delays on the developer edition, they usually launch a few months after the regular 15" while they sort new drivers.