The 4S is a 4 cell battery which ofcourse provides a wider voltage control range for controlling motor speeds. Battery current provides the torque needed to maintain the desired motor speed.
The depth and quality of the motor copper winding insulation is a function of the motor design voltage. If the voltage is too high, the insulation will fail over time.
The diameter of the copper in the motor windings determines how much current the motor can handle before the copper starts to overheat.
If your MR AUW - all up weight is low, you will not need as much current to remain in a hover which means the motors will remain cooler, longer.
If you need more throttle to maintain a hover because of increased AUW, that also means that you are pumping in higher voltages since voltage level is supposed to equate to motor rpm.
The torque/speed curves tell you everything you need to know and Ecalc for Multirotors also helps a lot.
In summary, you can often get by by upsizing the number of battery cells.... but I would never buy a used MR from those who do that..... the motor life has been compromised somewhat.
