hi if you have two rx packs the same mah-one 4.8v and the other 6.0v-the 6.0v will give you more servo speed and torque (holding power )always good things to have-if using high current draw servos like digitals higher mah packs at 6.0 v are advised (advised with NIMH BATS also )with digitals the centering torque will be increased with 6.0vyou will not feel any difference when flying the plane on the sticks as the servo speed are only increased from .16 to .13 seconds as an example and the torque is also increase somethe servo manufacturers list the servo speed and torque output for both 4.8v and 6.0vthe 6.0v packs do for some reason hold the full capacity charge in the shop for a longer time than 4.8v from my own experience-i have been told you will use up a 6.0v battery faster than a 4.8v battery of the same mahbut i myself have never found that to be an issue but that may be due to the fact i fly mostly 60 size planes 2-3 times a day at the field so my bats are never run down near there capacity DO ENJOY REGARDS TONY ''THE OMEGA MAN" THINK PINK ! ! !