1.2 volts per cell (under load) represents the midpoint of the discharge curve (50% capacity remaining) and a good place to stop and recharge. This is at 6.0 volts for a 5 cell pack and 4.8 volts for a 4 cell pack. Can you fly past this point? Sure but you are asking for trouble, as the prior gentleman stated, the voltage begins to fall off very rapidly below 1.1 volt per cell (knee of discharge curve). Better to be safe than sorry in my estimation.