Modern firepower against the Trafalgar fleet

What later warship could destroy the Franco-Spanish fleet fastest?

An Iowa-class ship with a nuclear shell is the extreme example; otherwise, a cruiser with rapid-firing five- or six-inch guns is suggested.

An Iowa-class battleship using a nuclear shell is suggested as an extreme answer to this hypothetical question. With that option set aside, cruisers carrying rapid-firing five- or six-inch guns are preferred. Their sustained fire is the relevant advantage against sailing warships.