Ok, I came across this forum while researching some 2nd hand Melton speakers I might buy, and by chance see one of my favorite topics, speaker cables.
I am an electrical engineer with way too many years up my sleeve, also started in the ham shack with my Dad when I was 5, he built all his own gear from scratch, including oscilloscopes transceivers, antennas etc, usualy with salvaged parts from TVs and radiograms - because I grew up in New Zealand in the 70s and no one had any money and thats how you did things.
So cut a long story short, there is one very important thing with speaker cables, and with all reasonable lengths it is not the gauge - I see comments about lamp flex - stranded lamp flex makes awesome speaker cables, some of the best there is. 1.5 sqmm is officially rated for 10 amps continuous based on heating losses and the temp ability of the insulation, also other factors.
But, let us say you are pumping peak 40 volts, at 10 amps that is 400W. That is a lot of noise, most people are not listening to anywhere near that much power.
Now I get to the point, copper oxide is a fantastic rectifier, before semiconductors were around, copper oxide rectifiers were a big thing.
If you use untinned copper wire and it is tarnished, the impact to the signal reaching the speaker will possibly dwarf eavery other imaginable aspect down to the use of maybe individual cat 5 cores, and even then provided the speaker wire is less than about 5% of the total loop impedance thru you 8 ohm or 4 ohm speaker, you wont hear it.
SImple version, there is more, but that is what you need to know.
Quite a few of the pull back, stick in the hole and bite connectors are ok, because they pierce the tarnish layer and form a sort of cold weld over time (look up how wire wrap works and why NASA still used it for years on space mission electronics).
But the screw down ones, even with the hole in the post, I am not convinced about a lot of them.
Anyway, tin your ends before you worry about just about anything else.
I am sure the new guy coming in here with radical ideas on one of the all time hottest topics in audio land (as I understand it) is going to get heavily flamed, but so be it, if it helps one person I will be happy.
Personally, I close my eyes and compare speakers/systems and if I cant hear the difference I don't pay for it, but years of heavy machinery make my ears now more cloth than golden.
Happy listening.