This completely overlooks the wonderful D-1541 (only 8 cores/16 threads) through D-1587 (16 cores/32 threads) series of embedded xeons that run at ~45W to ~65W compared to 115W of the E5-2670 (which this article says to run 2x of!).

http://ark.intel.com/products/93365/Intel-Xeon-Processor-D-1...

If you need just a ton of cores there are more efficient things out there! Not to mention that the D-1541 is available in Mini-ITX with 6 SATA 6.0GBps.

While I am not selling these things I have been drooling over them for a while, there are some great guides on tinkertry.com where they demonstrate this server: https://tinkertry.com/superserver-first-impressions.