Intel Xeon E5 2666 v3 's Advantages
Higher base frequency (2.9GHz vs 2.1GHz)
Intel Xeon E5 4660 v3 's Advantages
Released 7 months late
Higher specification of memory (DDR4-2133 vs DDR4-2133)
Larger L3 cache size (35MB vs 25MB)
Lower TDP (120W vs 135W)