If, for example, a ODP at an airport with a density altitude
at departure time of 4,000 feet, msl, and a required climb gradient of 280
feet per mile to 7,500, you determine with "certainty" that your bird can
do 300 feet per mile. Further, you cannot possibly determine the wind
direction and velocity with certainty in advance.


I would not depart - not enough margin of safety for me.