Xeon E7520 's Advantages
Higher base frequency (1.866GHz vs 1.8GHz)
Lower TDP (95W vs 185W)
Intel Xeon Gold 6421N 's Advantages
Released 12 years and 10 months late
Higher specification of memory (4400 vs 1333)
Newer PCIe version (5 vs 2)
Larger L3 cache size (60MB vs 18MB)
More modern manufacturing process (10nm vs 45nm)