The new system is what you want, cable and all. Yeah you want the cable a little long. I used Seastar's measuring directions and everything worked out fine.
Turn radius increase has not been discussed around the forum before in my presence. I do know that the helm and cable have nothing to do with a motors increased or decreased turn radius, it just pushes or pulls the steering arm on the motor and that's it. So that leaves the turn radius increase up to the motors tilt tube and steering arm. Knowing how steering systems work, I have no idea how that extra 10 degrees on both the push and pull stroke would be accomplished. A pic of that would be great.