Well, the smart money is on older decommissioned servers. Especially since Intel holds an advantage on plot speed. Even older Intel generations perform well on plotting, if you give them enough disk speed!
Also
I personally feel that 16c/32t is kinda the limit of what you should attempt to do on a single machine. It gets quite complex with more cores than that… 24, 32, 64 cores… balancing all that I/O is tough.