ORIGINAL: Silversurfer
Most of the current receivers on the market will handle more voltage than most think. However, none of the manufacturers will warranty any of their products if run at a voltage over 6.0. Using a freshly charged 6 volt battery, unregulated, will instantly void the warranty, but the receiver should handle it just fine. The choice is yours. If you need to dial in a specific voltage that's not 4.8 or 6 volts, I suggest a Fromeco SuperReliaswitch. You can adjust the voltage output from 5.1 to about 6.3 volts as needed.
I don't know where you are getting this information Pat, but Futaba rates servos at 6 volts, and if you tell them you are using a 5 cell pack for your receiver they will STILL honour their warranty. I know this for a fact, since I have done this exact thing. A regulator is not needed and simply adds another point of failure in the system if you are running a 5 cell pack. Yes, the hot off the charger voltage is almost 7 volts, but the pack has a NOMINAL voltage of 6.0 volts, and this is what Futaba is talking about when they rate a servo at 6 volts. I can't speak for other manufacturers, but I am quite convinced that they would be of the same opinion, in fact, I've seen JR branded 5 cell flight packs!
Jim