Here is some interesting information for you to look at.
You can look at the length of the run to where the servos are located. You can enter the wire size and the input voltage (6VDC) and the peak load you expect. It will then calculate the percentage of voltage drop and the available voltage at the end of the circuit.
For an example, if you use 22AWG wire (heavy duty servo lead size) and a run of five feet with a load of 5 amps you will see that the voltage will drop by .83 volts or almost 14%. The supply voltage would drop to just over 5. This would slow and weaken a servo from its 6V specs.
If you were going to build a power distribution system to provide power to the model in modular sections, (which it sounds like you want to) you should run some calculations for the main wire sizes. If you run a +- circuit back and do not size it correctly, you may as well just use the long 22AWG leads.
I hope this helps
http://www.bdbatteries.com/wirerules.php