My advanced civilization has finally managed to get gravitational engines to a smaller and more effective state. With this new technology, planes will now fly by 'falling' in the direction they are going. Steering is easily taken care of by changing the direction of gravity and can be done quickly. The pilots are also able to benefit from this, as the machines put the cockpit of the plane close to a 0-G environment, removing most of the G forces that would pancake the pilot in quick maneuvers and almost negating the human squishieness variable.
How fast would this technology allow a plane to fly/fall?