Solid gold single core stranded cable with cooling jacket to -170 degrees C
Any audiophile would be able to tell you that gold would make a [censored] poor cable. Copper has a conductivity of 5.96×10⁷ S/m at 20°C. for gold this is only 4.11×10⁷ S/m. That is significantly worse. If you want better then you go to silver which has the best conductivity of all metals 6.30×10⁷ S/m. You use gold to plate contacts because it does not oxidize and there is a trade off between surviving more insertion events with a thicker coating compared to it's higher resistance the thicker the coating.
For a low temperature superconductor then niobium-titanium would be the material of choice, For a high temperature supercondutor then yttrium barium copper oxide (YBCO) tapes are used. However none of these superconduct at -170°C. I would note that as long as you can cool it with liquid nitrogen the actual temperature at which it super conducts is largely a willy waving contest and things like current density and critical magnetic field strength are much more important than critical temperature.
Lanthanum hydride does superconduct at -23°C which would put it firmly in the realm of dry ice cooling. However it requires a pressure of 170 gigapascals which is even less practical that liquid nitrogen cooling.
The best idea is to use as short as possible a piece of wire and convert it ethernet as soon as you possibly can.