The silver jacks are actually tin or chrome plated brass (sometimes plated or stainless steel). The gold ones are just gold plated. The only difference is that gold does not corrode. This makes a slight difference for Hi-Fi gear, where the connecters stay in place for years, but for guitar cables this is a non-issue since you are regularly plugging and unplugging, and any corrosion gets scraped off in normal use. The idea that gold plated jacks transmit more low end is about the most ridiculous thing I've ever heard.