I've heard power cord shootouts on amplifiers, and differences are, to me anyway, quite subtle and it is hard to really compare cords because of the time it takes to make the switch. With interconnects and speaker wire, the comparison is MUCH easier to make--you can put one interconnect or cable on one channel and the other interconnect or cable on the other channel and then swing a balance control to easily make a comparison. I was surprised at how easy it is to hear a difference that way.
A local dealer who makes custom systems is currently experimenting with full range drivers in Karlson cabinets. This is at an early stage of development, but, he has been trying different speaker cables. While I knew from experience that Audio Note silver and copper speaker cables sound quite different, it was still shocking to hear how much different they sound when doing the left-right instantaneous comparison. Equally surprising was how different listeners reacted to the difference. Some liked the silver cables more (I personally appreciated the clarity and more explosive dynamics of the silver cable) and others, like me, preferred the copper cables (richer and better tonal balance for this particular speaker; the more attenuated dynamics and liveliness was not a big deficit to me because the speaker is so dynamic). In my own system, I use silver speaker cables, so if anything, I would normally be biased toward silver; but not in this case.