Help a noob? Please. BEC, ESC, New Servo for Flux.

[knuckle]

Confused here. I have an HPI Savage Flux HP. My life was not painful enough, so I decided to get back into RC. I have a Savage Flux HP. I've converted it to TCS 1/5 scale chassis. I'm replacing the servo as it hardly moves the wheels, and I have a $150 JR High Voltage, High Torque 7.4 Volt Servo

Now, I don't know much about electronics. I'm using all the stock electronics. The only difference will be the servo. What I'd like to do, to get the max torque / speed out of the servo is to use a 7.4 Receiver pack.

However since the Flux ESC is now powering the receiver, I'm not sure if I can just hook up a 7.4V 2s Lipo pack to the receiver. Do I need to disconnect the power from the ESC > Receiver first (red wire)?

Can the receiver handle the 7.4 volts? What is the stock voltage that the receiver gets from the ESC. I've emailed Castle, and HPI. No response in 5 days.

Do I need to use a BEC as well? I wish I knew what I was doing.

Any help appreciated.