On top of that ...
The dielectric constant changes with frequency (it is called dispersion). This was even a problem with 28800 bit per second modems. The signal for a single bit was spread all over the audio spectrum, and spread out in time between the customer's modem and the exchange. One proposed solution was to send many slow bit streams at the same time - each using a small amount of bandwidth centred on a different frequency. High speed optical links send many bit streams at different frequencies to counter dispersion.
If you sent an analogue signal over hundreds of kilometres of ethernet cable, dispersion might make a measurable difference. Back in the stone age, that is pretty much how the phone system worked. All the other sources of noise hid the effects of dispersion.
Some materials have lower dispersion than others, and it is possible to select pairs of materials that cancel out dispersion over a limited frequency range. For ethernet cables, lots of effort goes into reducing cross talk, but I have not seen any mention of dispersion.
The obvious thing these cables are missing is some carved amber end-caps so the electrons don't fall out while the cable is in the post. Only $1000 each - you know they're worth it.
Biting the hand that feeds IT
