Most of Futaba's equipment is made to be used with 4 cell alkaline packs this is the same voltage as a 5 cell NiCad pack (6 volts). As far as increased wear, if your servos have to generate their specified torque to move then you need larger servos. If you need 40ozin to move a control then you will be using almost 100% of a standard servo at 4.8 volts but only about 80% of the available torque with a 6 volt pack. While I usually loose this argument, if both are generating 40ozin then due to the conservation of energy the input power has to be about the same plus losses in the wires and servo amplifiers. Like I said, I usually loose this argument!