with a 2s receiver pack you will need to reduce voltage to 6, providing more components to fail. i don't know about all ESC's but tekin specifically warns against feeding the RS with 7volts from the receiver. KO electronics is good for 2s voltage but they seem to be the exception.
(my experience with voltage reducers have not been good. i have 2 for 2 failed. i had one fail at the start of the back straight on my gas car. if it had failed 1.5 seconds later it would have been very ugly. the lipo pack in my transmitter had a voltage reducer built in, which died while stored between races)
My Spektrum receiver is rated up to 9.6v. As far as I know Tekin is the exception and most stuff can handle 8.4v. People are running their Tekin's with 2s lipos despite the warnings and are not having any problems. You can drop the voltage to the ESC using
diodes if you need.