A 5 lb airplane must have 5 lbs of lift to maintain altitude. The heavier the airplane is the higher the AOA needs to be to generate the needed lift to maintain altitude. As speed increases the AOA needed to generate the needed lift decreases. Lift = drag and drag require power.

A high lift wing could reach a speed where a negative AOA was required to maintain altitude and that would waste power. That is the beauty of the symetrical wing for fast airplanes because it never reaches that point.