Uhh, 0m/s will give you the longest flight time. The faster you go the quicker your battery will be diminished.
Do you mean what’s a good tradeoff for moving? What speed allows you to travel the furthest on a single charge? Or how much extra range can you get by going slow?
Flightplan allows you to set up waypoints then long press on the line between waypoints and set the speed. Seems easy enough to set up a long circular route and then fly it at different speeds and see how long it takes you to reach 50% ( you don’t really want to fly down to 0, so 50% should probably give you a good approximation of your mpg vis a vis electric pixie usage ).
Personally I’ve been using sport mode to get to where I’m shooting, switching to film mode and shooting then back to sport when I’m done to get home before gravity starts to win.