Will My Heavyduty Metal Servos Run Better On 6 Or 7.2 Volts

@MovieMaker, I guess I can't be certain by what you mean about running better but I can say you will see a torque (strength) increase going from 6V to 7.2V. In terms of longevity you will probably see the servo have a longer lifetime by staying at 6V but as long as the servo is rated for 7.2V it should have a reasonable lifetime.

Thank You so Much!