Torque is the main reason we go 6V. Any given servo will output more torque at a higher voltage. That is IF the servo is designed to run on 6 volts. A lot of servos are not designed to run on 6V so you have to do your homework and make sure that the servo is designed to operate at 6V. Only bad thing is that 6 volts requires regulators and if you stay NiCad or NiMH you end up with a MUCH heavier battery pack. With more torque comes more current drain so those 5 cell packs need higher capacities and it just piles on the weight. Bottom line, in a plane less than say 11 pounds you dont need 6V. There are servos out there that operate well at 4.8V and put out plenty of torque like the Futaba 9202 or 9303's or whatever their new designation is... In your average sport or 40-60 size 3D plane you dont even need that much, about 60-75 in/oz is plenty on 4.8V.

We use 6V in our giant scale aerobatic planes because we need more powerful servos and lots of them. I am running 9 servos in my newest 35% Extra 260 8 of those are Hitec 9151 Titanium geared servo's. They put out 333oz of torque [8D] at 6V and I need every bit of it. I run this on 2 4400mah Lithium Ion (this powers servos, receiver and ignition) Battery packs from www.Fromeco.org . These guys sell some fantastic Lithium packs at a great price. Dont let people scare you away from LIthium Ion either, they are becoming more and more widely trusted by serious competitive RC hobbyist. They are lighter and mah for mah will last about twice as long on a charge than NiMH or NiCad. The Fromeco packs are holding up too. To give you a rough comparison.. on a charge with 5 cell NiMH packs I can get 3 flights and I must recharge. On 1 4400mah LIon pack I can get as many as 12 flights and then I only recharge because Im afraid not to. [8D]