<font size="3">In the case of the Spektrum DX7 and the DS821 servos, going to a 6 volt battery will also provide a higher torque.  I believe it's 72 Oz torque at 4.8 and 88 oz torque at 6 volt.  So if your airplane requires a higher torque, you really should be using a 6 volt battery anyway.  Just make sure to get a higher capacity as well so as not to shorten your flight time.   My latest project requires 80 oz torque so guess what voltage battery I'm going to use.  4.8 is what the manufacturers provide because it works for most applications but ...</font>