Originally Posted by RONALDO_UK
By the way, I presume I was at least right in saying the ESC controls the current (amps) delivered to the motor (must do, it certainly doesn't control the voltage)?
No. the ESC merely passes through that what is demanded by the motor based on the voltage and the load (prop).
If you have too small an ESC it will limit the throughput before it burns up.
Too large does not improve things, it just weighs more and costs more but is less likely to burn up if you screw up. It may run cooler, but if you've sized right about 20% larger than the maximum output of your prop/motor combo in the voltage range required will do fine.