Not sure about small size heatsinks, but copper heatsinks are better in general and cooler tests on FrostyTech prove that just fine. Just take a look at Zalman copper and aluminium versions of their coolers for instance. Perhaps copper is only better when combined with active cooling such is a fan.

In this case it doesn't matter and the V2 doesn't put that much heat, there are still chipset coolers that are thin enough to fit that will allow the card to remain as a single slot but still get the job done. If you want to go fancy just go all copper if you don't mind the cost. I did this to a Voodoo Rush.

Since all of the affordable listings come from Asia, I have to wonder whether the heatsinks are actual copper, an alloy, or just copper-tone. I wonder if there is a simple way to test this with an inexpensive chemical. Would be interesting to find out.

If they are heavy they are copper, the copper plated coolers always have an off color to them in person and they feel very cheap. My advice is to find a good seller and go from there.

I'd used aluminum.
And a lot of cheap copper heaysinks are anodized aluminum or plated

Best way to tell is to scrape the heat sink a good bit. If you see aluminum it's aluminum.
aluminum Heat sinks are often harder too, copper heatsinks tend to be soft.

I scratch the side of all orange coolers that come into my hands. If it's metal white inside, it's definitely alloy. Most are alloy 😀

It does not matter much as I see it, the alloy heatsinks with developed surface will have better heat dissipation, while copper heatsinks with smaller surface will have better conductivity. Anyway, interface quality should have more effect then both heat dissipation and conductivity.

Btw, copper heatsinks take more time and heat to heat up, being more massive and having more heat capacity, but I would expect them to be hotter when stationary compared to alloy heatsinks with developed surface.

It's aluminum, oldest trick in the book that china uses is to anodize aluminum a copper color and sell it as copper.
From what I know anodize aluminum sinks tend not to do well as there cheap junk, but they do look cool.