Speculate, in terms of the microscopic surface irregularities, about why µk< µs, and what effect a lubricant has on the coefficient of friction.

Any surface, when observed under a sufficiently powerful microscope can be seen to have a lot of irregularities (Refer to the attached figure). When two such surfaces come into contact with each other, given adequate amount of time, the irregularities can interlock quite well with one another. Thus, in the case of Static Friction, because the surfaces are not moving relative to each other, the irregularities interlock very well, thus requiring a greater amount of force to dislodge one object from the other.

On the other hand, when an object is moving, the irregularities are not given sufficient time to interlock well with one another and hence, lesser force is required to dislodge one object from the other.

Under such a scenario, we can intuitively understand that when a lubricant is put on a surface, it would occupy the spaces left by the irregularities, thus filling them and not giving a chance for another object's irregularities to interlock. Hence, we see this as a great reduction in the overall friction force.

most voltage drop calculators want the distance between the source and destination. then internally, they double it so both the source and return wires are calculated. but you need to know which distance the calculator uses so you're not half of what you should be or double what you should be.

most circuit breakers will not take a #6 directly, so the electrician will have to splice on a smaller pigtail. you also have to upsize the grounding wire when you upsized the ungrounded (hot) wire (see note in 250.122). this will preclude using most cable assemblies, as a cable with #6 copper will most likely only have a #10 grounding conductor. you need a #6 grounding conductor if the circuit is 20a. a #8 cable is no better, as it will have a #10 grounding conductor too. but most 20a breakers will take a #8 directly.

in your related post, you didn't say what type of load this is. if it is a light or heater, voltage drop won't be a big issue. if this is a motor, the current needs are huge at startup and the voltage drop can pose a problem. if this is a motor, knowing if the motor is under much load during startup will answer the voltage drop effect (a saw is easier to start than a compressor).