RE: High amp 5955 servos
Typical amp draw is only like 2-3 amps average on a 35% plane, assuming no servos are fighting each other and the engine doesn't vibrate more than normal. Max amps it will typically ever see is 10 amps or so, and that is usually only in short spikes, like in a snap or blender, and such.
With your setup, three leads are fine, but you probaby should plug all four leads in to balance the current distribution. You can "Y" that extra lead into any open channel without consequence, except maybe the slight voltage loss through the additional connector.