From what I understand he voltage doesn't drop that easy. It takes a little time. If you were running an electric motor you would want to use NICAD instead of the NIMH. The NICAD would last longer in this case. Maybe we should do some research and see where the two curves cross. Find what point they cross and at what kind of load makes one better than the other.

PS the RX goes into failsafe when the battery is low(just pulling the plane to idle and can be brought back up by cycling the throttle) They say you don't get a complete lockout until about 3.7 volts, but I have flown down to 3.62 volts before. At that low voltage I was getting intermittent lockouts when I feed movements, perhaps when it was at neutral the drain was not enough to drop below the 3.7 threshold.