Yes, I understand those differences, they're often quoted and can't be denied. Purer copper is a better conductor (of electricity and heat - so nicer for soldering).
Greater cross sectional area also means lower resistance, allowing for greater current carrying capability.
When I asked about discernible differences, I meant in what you hear.
I know what you think, but you don't know whether I've witnessed sound quality differences with speaker cables or not
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See with respect, it's easy to say things like 'as long as the cable can handle the current' Sceptics would ask how much current is involved and how much current do you think a 2.5mm cable can handle. Quite reasonable questions.
Mind you, unless I'm mistaken, your final sentence:
'At the end of the day if you have a good conductor (pure copper for example) of thick enough gauge, then over a reasonable distance (say the typical distances from amp to speaker, say) there will be no perceptible differences in attenuation across frequencies'....would seem to suggest that cable brand is unimportant - now that's where a lot of people (by no means all) would agree.