Every Hitec servo I've ever used works with 6V or 4.8, you get a little more speed & torque @ 6v, no regulator is needed (again for Hitec anyway.) I often use a mix of digitals and non digitals-digis on ail & rudder, standard on elevator halves. It works well enough for me, can do most 3-D with this configuration. I have a U-Can Do with all HS635 Karbonite(6.60 size), with a few mods to the plane, I can do everything with these standard servos,the rollling harriers are very slow(but kind of cool I think because of that)but everything else is good-hovers,harriers,walls,no problem with standard servos & 6Volts.