I'm going to pull the top on a servo and check the voltage with the esc powered up and see what kind of voltage there is. i think the circuit board in the servo has the voltage regulator.
You'll have to wait for someone else's opinion, but I don't think so. I know you can get digital programmable servos that can be set for speed, torque and a few other things, but I seriously doubt you can up the voltage through the ESC.
More than likely you will see a pretty dramatic increase in power. Just like going from 4.8 to 6 volts. The higher quality cells, the more you'll notice.
You can disable the the BEC on your ESC and run an external BEC that has adjustable voltage output. Castle Creations makes one that is adjustable via their Castle link cable and software.
You'll also want to check that your receiver can handle the voltage. Spektrum receivers and a few others can. Also, not all servos can handle the additional voltage.