I don't have the experience Acuujim has with the Select series, but I will note that in my system the Kimber Silver Streak (copper/silver) clearly was not as good as their similar but all-silver KCAG. While the bass was virtually the same, the KCAG had a far better upper midrange and treble, with more delicacy and air than the Streak, which sounded brighter and more course, for lack of a better word. Not earth-shaking differences, to be sure, but I preferred the KCAG in a full-range application.
