terpster, I sence a bit of irony in your post..
GS is irrelevant when considering your requirements.. surely
IE.. for a given TAS you will get a given value of Lift assuming all other factors remain constant. ( Your V speeds are surely not derived from GS)
For the certification the demonstrated gradient to be achieved on climb out is a still air gradient..
Hence the climb gradient in your WAT CLIMB limited graph is also a still air gradient..
In order to achieve obstacle clearance and calculate your flight path over the ground, wind is obviously a factor.
It Am I falling of the Iron Rails in the sky, as you describe them ??