So, this is what I have found. (Though, correct me if I am wrong.)
It looks like the all copper Heat-sinks are really good heat conductors. But, they aren't as good at dissipating that heat into the air as Aluminum.
So, if that's true than the ideal Heat-sink for CPU's would be copper base plate with copper pipes and Aluminum fines to dissipate the heat faster.
Someone also brought up in one of the threads, the idea of a chart that shows how quickly the CPU's are heating up and cooling down between stress tests between the Aluminum C7 and Copper C7. But, it doesn't look like anyone has collected that data just yet.
Not too many good AM4 comparable heat-sinks out there unfortunately. As of now the two best are still the L9a and C7.
Hopefully, that HSLP-48 cooler can deliver to offer another good option.
The LP53 and Titan NC25/NC75 look interesting. Seems like the Titans are very much favored but require the fan to be replaced with a Noctua for best results. However, the Titans are listed as "Universal" coolers so I don't know how easy it would be to make them fit a AM4 mount. Let alone simply find one for sale in-stock.
Very little information of the LP53. I remember seeing some promising test results for it but not much else. Again, swapping the fan for this one to the Noctua is also recommended.
https://www.titan-cd.com/en/product...and-1.5U-Height-TDP-130W/TTC-NC25-Series.html
http://www.cooltek.de/en/cpu-cooler/lp53/128/lp53