RE: using two battery packs
What kind of plane is it that you need that big a servo for the rudder? I'd definitely increase the size of your battery, at least 1500mAh.
That's why I was asking about high torque or digital servos, NiMH aren't recommended due to the current drain; if you parallel the packs, though, it halves the internal resistance of the system, and generally NiMH is okay. The newer ones can deliver current better than the older packs could. I have an old beater gas powered plane that has 3010 Futabas (2) and some kind of old 1/4 scale Futaba servos (2) plus a standard servo. I have a 1000mAh NiCd battery in it which needs recharging before I can run a tank of gas through the engine, so I can say for sure that 700mAh ain't enough ('course you know that or you wouldn't be asking about two packs).