Generally how I do it.. Bigger the motor bigger the esc... To be honest unless I have weight or size restrictions I go 160 for 700..
120 for 600/570..
100 for the new 500/380..
60 for 360

But that's just generally how I go.. Tho I have a 120 in the e700 right now

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An ESC should be rated for S (voltage) of Battery and exceed full load amperage of motor..... right?

 

The rule of thumb I got told, get your max motor amperage, add 25% onto that, then get an ESC which exceeds that.

However it might be worth looking at max burst current of the motor and ESC. After all, for electronics it only takes a split second to cook things.