Hi Bungle, bench running, and what happens in the water, are two different things, and vary according to the volts you are using, the prop size and type, and how good the drive line is. Always try and give yourself some headroom with the esc, the packaging of the motor (or google results) will give you an idea of the suggested max amp draw, and the stall amps, then you can make a judgement on the esc.
I use more than 10 amps on my lights!
