You hit the nail on the head there, it was mainly the length of the back of the jacket. The gamekeeper is quite a bit longer which is great for when sitting on rough ground while I knock up some bacon sarnies etc😁 One other thing that swayed me was the under arm zipped vents on the Gamekeeper. I have these on one of my Mountain Equipment jackets and use them quite a bit. The lining isn't exactly what I was after but (wanted more of a quilted lining) but it's a compromise I can put up with for the other benefits.