The science of superconductivity deals with superconducting materials, and temperature factors into it because at temperatures approaching absolute zero atomic activity slows down significantly, allowing tunnelling effects to motivate electron currents to travel almost without friction. This is extremely important. For a constant current of 120 amps (the size of the main alternator fuse in your car), a wire CM of 105535 (0-ga wire), the voltage drop on a 12' wire would be about 0.144 volts (
found here). That really adds up over long distances, and that is why we have an electrical grid that distributes power over international boundaries, because we simply can't conduct electricity over very long wires economically. Superconducting materials in testing over distances without coolling are approaching the desired behaviour. Vacuum has nothing to do with it, so why even bring it up?