Ok well I was supposed to be getting copper heatsinks but they sure look brass to me. Unfortunately I didn't pay close enough attention when I got the sample so I didn't catch this until a large box of them showed up at my door and now I am stuck with them.

So I did some tests using a 5w led to compare between the new and old heatsinks. After 20min the aluminum heatsink was actually 2 degrees hotter than the new heatsinks. I did this test on the bench using a thermometer inserted into the bottom of the heatsink. Some of the heatsinks show copper spots on them so I think the metal is some kind of copper/brass mixture??? I will try and find out from the manufacturer exactly what the metal is.

Either way they are all I have for the time being and they seem to work fine to me so its what I will be shipping for now. If anyone can do a better test and has contradicting results please let me know.