RE: ESC/BEC needed for a brushless motor using a NiMH pack?
Yes. There are ESCs for brushed motors and ESCs for brushless motors. They are completely different, and you must use the correct type for your motor.
For your Speed 600 brushed motor, you must used a brushed ESC. Later, when you switch to a brushless motor, you will need a brushless ESC.
You will be able to use your NiMH battery pack with either type of ESC.
- Jeff