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I hear older Intel Xeon servers (in 19" rack mount cases) do pretty well at Cryptonight mining; I might pick up a few to find out as GPUs are insanely expensive right now.
Cryptonote in general does well with 2MB of cache per 1 core for mining. So if your CPU has 4MB cache the best setup with be 2 Threads for mining. Xeon's do well because they have a lot of cache.
Yep, that's my understanding. I'm toying around with the idea of setting up a little server farm specifically for DERO and another Cryptonote coin, eDollar.