The difference is the higher rated voltage cap has more material inside and they will be bigger for sure, More material is needed for handling the increased voltage. Speaker uf values are larger and meaning  600uf versions of 12uf caps would result in caps that are giant sized. They still can be at 100v 😊
They can and and often do sound different. A 300v and 600v version of the same cap can indeed sound slightly different. They use the same materials inside, but more material can have a slight impact on the sound. Over on the Humble  Capacitor review site they often pick up slight sonic differences in caps that have both lower and higher voltage ratings.  It depends on the cap. Higher uf values are usually not even offered in the higher 600v option however.Â
They can and and often do sound different. A 300v and 600v version of the same cap can indeed sound slightly different. They use the same materials inside, but more material can have a slight impact on the sound. Over on the Humble  Capacitor review site they often pick up slight sonic differences in caps that have both lower and higher voltage ratings.  It depends on the cap. Higher uf values are usually not even offered in the higher 600v option however.Â