Subwoofer Cables. How important is quality?

I have been wondering if I need to upgrade my AudioQuest Cinema Series cable. I have mostly Cardas Golden Ref IC's in my system, so I contacted Cardas and they responded that they don't really emphasize any particular need in the sub cable due to the frequencies. They don't make a subwoofer cable that is labled as such, but I notice many cable mfg's do. What is the belief in AudioGon Land? Is there any concern with the low freq's for sheilding or cable construction? Some say silver is better to add speed, some say copper is better.