Intel Xeon E5645 's Advantages
Lower TDP (80W vs 135W)
Intel Xeon E5 2666 v3 's Advantages
Released 4 years and 8 months late
Higher specification of memory (DDR4-2133 vs DDR3)
Newer PCIe version (3 vs 2)
Higher base frequency (2.9GHz vs 2.4GHz)
Larger L3 cache size (25MB vs 12MB)
More modern manufacturing process (22nm vs 32nm)