Mirkoskji I remember that extending copper to fins in big heatsinks was not bringing Big performance benefits in the past. Did the overall design improve to take better advantage of this feature?

It doesn't bring big benefits, no.There used to be a bunch of voodoo people would spout about aluminium having better "emissivity", and therefore somehow being better. That's complete rubbish and you should ignore anyone spouting it.The explanation I've always found made the most sense is this one:If you could magically somehow heat one copper heatsink fin and one alu heatsink fin to exactly the same temperature, say 40C, in an ambient of 21C, and you blew a fan on them, the amount of heat moved off of each fin would be identical. The material used simply doesn't matter in that way. Each molecule of 21C air would pass over something 40C, pick up the same amount of heat while doing so, and then blow away into the room.Thing is, heatsinks are not heated evenly across their whole surface like that. You can't just poke a heatpipe through a piece of metal and expect it to heat that metal evenly across it's entire surface. The heat will conduct outward from that central point and so the area next to the heatpipe will be hotter than the ends of the fins.The longer you make the fins, the further it has to be conducted away from that heatpipe. After a certain distance, adding extra length to a fin makes no difference, because the heat simply never gets there before it's dissipated by airflow. You can increase that distance by using a material that conducts heat more quickly along it's length - like copper.Additionally, if you do this, then the distribution of heat along that fin ends up being more even. By this principle, an all-copper heatsink can have longer fins before that impacts performance.The greater the delta between ambient temperature, and the temperature of a dissipating element, the faster the transfer of heat between that element and the air moving across it. Since the Cu heatsink will have a greater delta over a greater portion of the fin, it therefore acts similarly to as if the heatsink had more surface area -For this reason, at least when the medium of heat transfer from the IHS is a heatpipe, large all-copper heatsinks do perform slightly better than large Copper/Alu heatsinks, but small heatsinks will show a smaller difference in performance between these two approaches.