I have argued that higher voltages do give you shorter discharge times with the same capacity but when used in a flight pack, the increase speed and power of the servo should make the servo get the position 25% quicker on a 5 cell pack compared to a 4 cell pack. With this said, the flight time should be the same. Many people disagree but no-one has been able to take the realities of our flight dynamics and convince me any difference.