Motors - high voltage/low voltage??

[RONALDO_UK]

Hi - I'm not sure if this question belongs in this forum, "Beginners", "Power Systems" or all three??
I know the kv value of a motor indicates its rpm (dependent on voltage applied) and some motors can utilise a 2S or 3S battery - is the motor always turning at this speed (V x kv), regardless of how much power is supplied? And if the same power is supplied by each battery, am I right in thinking that with the lower voltage (lower rpm) battery, the compensatory factor is more thrust/ torque?? If weight is not an issue, is it always preferable to use the higher voltage battery (to give extended rpm/power) - provided the permissible current draw of the motor is not exceeded??
Regards.