AussiePilot,

The bottom line is that you can use EITHER type of battery AS LONG as they are the same voltage output. The reason for these is simple basic electronics. Current is equal to Voltage divided by Resistance, SO.... as you increase voltage you increaase current. For that reason when you use batteries of higher voltage than the recomended output, one nust DERATE the current carrying capacity of your system.

I bet than in this case LiPos of too high a voltage were being used to drive a whole bunch of power hungry servos. If you check some of the new high torque digital servos. For example a Hitec HS-5995TG specifications for Current Drain (6.0V): 300mA/idle and 4.2 amps at lock/stall
Current Drain (7.4V): 380mA/idle and 5.2 amps at lock/stall. If you use a three cell Lipo (11.1V) regulated to 6V, and a couple of this servos get locked at maximum current drain, you will get arround 20Amps of current through your batteries, and some smoke will be produced.

My final recomendation is. If you are going to use the Duralite Power System, STICK with Duralite batteries. I am not sure, but a friend of mine that was using their system ruined the Duralite batteries by using a different charger than the one they recomend. He mentioned the Duralite Batteries have some type of power guard wiring system to protect the baterries from overdischarging, and possibly to balance the charge throughout all the cells. In any case if you are going to invest in a very expensive system like Duralite, what the heck is the difference a few more dollars in batteries. By the way I think it's a waste of money to equip any plane smaller than a 33% with such expensive system and servos. Any good servo isolation system and power regulation system will do, and for a plane of this size good quality metal gear 100 oz/inch torque servos per surface will do just fine. And unless you are a an extremely acomplished 3D pilot, running those superfast coreless digital servos you will need a whole bunch of negative exponential for sport flying