Actually, unloading the elevator makes a plane go faster. In normal flight, the tail surfaces must provide a down load (negative lift) to hold the planes nose up & that down load comes from elevator or wing-tail incidence --- it creates drag. Unloading the tail, as in the example that you just gave, reduces tail negative lift (it is still lift) & reduces drag. That is why "tail heavy" planes go faster than "nose heavy" planes.

Flat bottomed airfoils are often faster than symetrical, or semi-symetrical foils, for all of the noted AOA reasons.