My experiences FWIW....
I stopped messing around with speaker cables many years ago, the reason being I found cables (Naim) that suited my system after trying about 4 name brands and a few experiments with ordinary mains cable. Huge differences between all of them. Cables probably have improved over the years so there's not as big differences now, but if you can't hear the difference between a heavily stranded cable and single core there's a problem, probably hearing or speaker quality. I've always wanted to try 15mm copper pipe but one has to stop somewhere.
I never could hear hardly any difference between interconnects though. I borrowed silver ones once and they had a bit more upper treble but not what I would call an improvement. I found a huge reduction in headphone sound quality when using a coiled extension lead - all the space vanished, a closed-in sound resulting.