RE: GY401 and RX battery
You can burn up the servo or at the very least shorten its life.
Duralite makes a step down that you can put inline to the gyro that acts like a mini regulator but as I said there's no good reason to run 6volts. If you want redundancy incase of a cell failure go ahead and get Li-Ions that are 2s2p with a switch safe regulator then you have it all covered plus 8 to 10 flights per charge.