The advantage of gold is it will never corrode. But its conductivity is rated at .95 where copper is the standard of 1.0. Silver is 1.05. Silver can tarnish where the tarnish is still conductive but resistive too. When cooper corrodes that is an extremely high resistance.
That being said I have a 23 year old pair of copper speaker cables (99.9999%) and although it hasn't corroded yet the copper ends (bare wire) does get discolored. I cut back 1 to 2 inches every 4 or 5 years and all is like new again. Even though I still have those cables I don't currently use them. I upgraded to the Nordost Frey's which are silver plated and polished over 99.999999 copper AND sealed so tarnishing should not be a problem.
Last all metals will sound different so go for the sound that you want. I wouldn't worry about how long they will last.
That being said I have a 23 year old pair of copper speaker cables (99.9999%) and although it hasn't corroded yet the copper ends (bare wire) does get discolored. I cut back 1 to 2 inches every 4 or 5 years and all is like new again. Even though I still have those cables I don't currently use them. I upgraded to the Nordost Frey's which are silver plated and polished over 99.999999 copper AND sealed so tarnishing should not be a problem.
Last all metals will sound different so go for the sound that you want. I wouldn't worry about how long they will last.