Paul,Hi MickCable measurements can tell us more than just impedance, or DC resistance. As S2000db has said, the only noticeable audible difference in two cables with differing resistance could be a slight volume difference. I'm sure you've seen the articles on cable manufacturers demonstrating their cables against a "standard" cable where during a show, they'll craftily turn the volume down when demonstrating the standard one and then turn it up a tad demonstrating theirs so that the audience will "hear" more detail etc. Some cables are quite high in their capacitance and depending on the output and input impedances of your kit, a high capacitance cable can rob a system of some top end detail. For those with perfect hearing, they may be able to detect a few dB rolled off above 15KHz so that cable may be the one to "tame" bright systems. For most though, there's little evidence (that I can find anyway) that even a 1m pair with say 250pF capacitance makes much difference in most systems. The single greatest impact on how a cable sounds IMHO and experience is its S/N ratio. Two identical cables with the same resistance values to the signal core could sound very different if one is poorly screened and the other is well screened. There's a misconception that screening is only needed or of benefit in noisy environments but as (more) importantly, the lower the screen (or signal return) impedance, the better the S/N ratio and for a given capacitance, in theory the more dynamic range and detail you'll hear. Most differences in commercial cables are down to S/N ratio and perhaps that's what most people hear as differences. The minimum accepted hifi standard is an S/N ratio of 100. I've made cables ranging from S/N of 90 to 140 and there was an audible difference between them in my system. Hopefully this explains why calculations or measurements are still valid when comparing cables.
Firstly, I am unaware of any standard for S/N ratio so why 100dB? Perhaps because that's better than CD provides, but why not 103dB or 110dB?
Secondly, the S/N ratio depends both on the N and the S, and as the N is fixed for any one cable or installation, it then depends on the S. A bigger S will provide a bigger S/N ratio. Unless you mean something different by N, like the thermal noise in the cable.
Noise pickup will depend on the field strength for the interfering noise, the impedances involved at both ends of the cable, and of course on the amount of screening. This is effectively per unit length, so a long cable will pick up more interference than a short cable, which is why long cables are preferably balanced.
There have been integrated amplifiers with very short unscreened links between pre and power sections, and yet the S/N ratio of the amplifier is unchanged when removing the unscreened links and replacing these with a length of screened cable. If screening affected the S/N ratio, I would have expected it to me worse with the unscreened links.
S.