Good point old smokey - 1st segment would give you a feel for how it would go if the double-failure situation arose, i.e one quit at V1 plus the gear stayed down. But it would not be the basis for planning a ferry with the gear down, for as you say it is useless information at later phases of flight. I can't find it in any of my old and now very superseded manuals either. Next time I am anywhere near a real airplane I will try to find it in the AFM, but even then, different countries sometimes include different appendices with the AFM.