Carbon is actually an excellent choice for interconnects, with one caveat: they must be short cables.
Conductivity is actually a low priority for interconnect metallurgy. In order to get uniform current flow across frequencies, I believe that metals must have optimum and undisturbed crystal lattice in the metal. This is why ultra-pure silver, copper and gold work well. Gold is the best choice in metals because it is the most malleable. This means that the crystal lattice stays intact even with a lot of bending.
I proved this assertion by building two identical cable sets and then immersing one in liquid nitrogen to break the crystal lattice of the silver wire. Then I made a TDT measurement on both cables. The trace shows an obvious breakage in the crystal lattice as many more reflections are evident in the immersed cable set versus the non-immersed cable set. L, R and C measurements did not change, as expected. Listening tests also showed that the immersed set sounded terrible. I think a hanger wire would have sounded better.
Carbon does not seem to be a sensitive to crystal structure as metals. Current density across frequency seems to be more uniform. The only downside is the resistance, which can be a problem in some systems, and depending on length of the cable.
Steve N.
Empirical Audio