The crap servo in my rc82e rtr has to be replaced. I'm looking at specs for servos and they give different performance at different voltages.

I assume my servo is being powered through the Rx which is powered via the ESC.

Do I have to have an ESC that supports sending different voltages out to the RX and then in turn to the servo? I don't see anything about sending different (or even any) voltages to the electronics in any of my documentation.

You're on the right track. The most straightforward approach is to compare the 6V servo ratings, they are available with enough performance for most from a variety of brands. Generally 200 or more oz-in of torque and 0.15 second for 60 degrees or quicker performance is considered adequate for a 1/8 by many. With metal gears.

If you feel the need for more performance, either need to add an external BEC at a higher voltage, or switch to an ESC that offers higher voltage BEC operation. Requires a high voltage servo in most cases (some regulars are known to work OK too). A receiver that can handle the higher voltage makes it easier, but is not absolutely required, at least for the external BEC approach.

Also be aware that some servos, notably at least some Savox models, may require an external BEC even at regular voltages.

After doing some reading on what a BEC is, I believe I will go ahead and get one.

Would you mind posting a few recommendations? I'm looking for 7.4v output and using a 4s. I see a pretty good range of prices on these things.