In my opinion even tho metal purity is important (as confirmed by recabling the 15 inch of wire between my midrange/tweeter passive crossover with Neotech UP-OCC wire) in the grand scheme of things, geometry, choice of dielectric, choice of solid core / multi strand etc will have a huge impact as well. What matters is the final result. I use Chinese cables, whose metal purity is impossible to know for sure, but the geometry and decision to use multiple individual solid core wires, individually isolated, make those the very best speaker (and interconnect) cables I’ve ever tried and / or owned.
I’d also say that "thicker is better" is very far from being the truth, depending on your loudspeakers, the opposite can often be true. I believe thin solid core wires give more resolution, details and dynamics than a thick multi strand wire, no matter how pure the metal is. YMMV, as always, but in the context of my system it definitely is the case.