Thank you, Hoppy and Ater.
Sheesh.
There must be fifty ways to define gradient ( cheap reference to Paul Simon's song).
The big thing is not to contact Mother Earth. THAT is where the "gradient" comes into play.
RoC is normally a constant for power, gross weight and AoA and such. That's in the air mass. Over Mother Earth, it's a different story.
You are making this more complicated than the original question, Highfly.
If the chart says you must achieve "x" feet, "x" miles from the runway, then I would look at my plane's performance and the appropriate charts for my plane.
This thread is getting old, and I am not sure we are satisfying the questions that Highfly started with. Many of us here have thousands of hours, and I flew many right at the limits of the aircraft performance. If one can not trust us to provide an decent answer, then who else can?