Xeon E7520 's Advantages
Higher base frequency (1.866GHz vs 1.7GHz)
Lower TDP (95W vs 105W)
Intel Xeon E5 4648 v3 's Advantages
Released 5 years and 3 months late
Higher specification of memory (1866 vs 1333)
Newer PCIe version (3 vs 2)
Larger L3 cache size (30MB vs 18MB)
More modern manufacturing process (22nm vs 45nm)