Intel Xeon E5 4640 's Advantages
Lower TDP (95W vs 135W)
Intel Xeon E5 2666 v3 's Advantages
Released 2 years and 6 months late
Higher specification of memory (DDR4-2133 vs DDR3)
Higher base frequency (2.9GHz vs 2.4GHz)
Larger L3 cache size (25MB vs 20MB)
More modern manufacturing process (22nm vs 32nm)