Should also make it clear, the 2.7 and 5A will hold -
That just indicates an inadequate power supply. Servos under load (or starting current) can use more than 1a each (probably more if they are large servos). Also most servos have a lower operating limit of 4.8v. Lower than this and digital servos in particular may have control issues. People uising lipo batteries are able to operate hexapods with 18 servos.