Intel Xeon X5660 's Advantages
Higher base frequency (2.8GHz vs 2GHz)
Lower TDP (95W vs 120W)
Intel Xeon E5 2686 v3 's Advantages
Released 4 years and 6 months late
Higher specification of memory (2133 vs 3)
Newer PCIe version (3 vs 2)
Larger L3 cache size (45MB vs 12MB)
More modern manufacturing process (22nm vs 32nm)