Intel Xeon E3 1220 's Advantages
Higher base frequency (3.1GHz vs 2.2GHz)
Larger L3 cache size (8MB vs 1.5MB)
Intel Xeon D 1520 's Advantages
Released 3 years and 11 months late
Higher specification of memory (DDR3 vs DDR3)
More modern manufacturing process (14nm vs 32nm)
Lower TDP (45W vs 80W)