I have compared MANY 8-12 awg COPPER cables (some OFC and some none OFC but never copper clad) & various fuses (thats a different story) but never spent to buy silver cables.
With the copper cables, I noticed NO difference whatsoever. My typical speaker distance is about 6-7 feet or so from the power amps. At that distance, the difference in resistance between the copper & silver cable would be less than 0.01 ohms. As I said, the brass connectors on the speakers would have more resistance than this.
Seriously ......