The first flight aircraft that flew yesterday (and the other test aircraft) are both the freighter model.

Both the passenger and freighter version are stretched 5.6m(18.3ft). Both have a 1.5m behind the wing and a 4.1m stretch in front. On the freighter, the stretch is behind the hump (and actually includes the area where the wing mounts). On the Passenger version, the front stretch is just behind the upper deck emergency exits. so your adding ~8 windows upstairs.

[EDIT]...and Jack beat me to it....[/EDIT]