Technical brushless motor ?

[kostaktinos_mt]

'load' is defined as: vehicle weight,rotating mass [mostly weight of wheels&tires], aerodynamics,etc.
thus gearing, is the means of manipulating/harnessing the load related to the motor.
a lower kv [sometimes physically larger too] motor with higher voltage is more efficient and consumes less current [thus allowing you to work with 'smaller' batteries].

however, keeping the same load [and motor and gearing] and doubling the voltage, will decrease the efficiency and will require better batteries.

assuming same genre motors and same vehicle, and without being too technical, you can say that:
a 4000kv motor with a 3s battery and geared at 20/60 [example that is], is less efficient and needs a 'better' battery than a 2000kv motor with a 6s battery with the same gearing [20/60]. also notice, that the top speed will theoretically be the same, while runtime and working temperatures will be different [due to the overall efficiency difference].