RE: 4.8v vs. 6v receiver batteries
I don't run a voltage regulator and have never seen any reason to, including after talking to Andy Low, the owner of ElectroDynamics. The servos - unless they specifically state that they shouldn't be used with 6v batteries - have no problem operating at the typical voltages slightly over 6v such as I have ever encountered.
Make sure that you don't discharge the batteries too far! I believe that you shouldn't let them get below 1.1v per cell, meaning 5.5 volts for a5 cell battery when discharging. Are you using a cycler? If not, you may want to consider getting one as this will allow you to keep track of all your batteries as they are used and age, and allow you to cycle them in the off season - always a good idea.