Xeon E7520 's Advantages
Lower TDP (95W vs 115W)
Intel Xeon E7 4809 v3 's Advantages
Released 5 years and 3 months late
Higher specification of memory (1866 vs 1333)
Newer PCIe version (3 vs 2)
Higher base frequency (2GHz vs 1.866GHz)
Larger L3 cache size (20MB vs 18MB)
More modern manufacturing process (22nm vs 45nm)