ORIGINAL: Dr1Driver
I've used 6v battery packs for many years with NO regulators required. You get 20% more power and speed and about 20% less flying time.
Our electronic equipment can handle a fully charged 6v pack easily. ALL electronics are built with "overhead". That is, an RX rated for 4.8v doesn't have 4.8v components. Standard electronic parts are rated for standard voltages like 15, 24, etc., which are usually higher than the voltage used by the device they're in.
Dr.1
Some, not all, Futaba servos are limited to 4.8V input. IIRC, this is mostly limited to their less expensive "sport" digitals, and I'm not sure exactly where the limitation came from, but it is called out on their spec sheet.