Intel Xeon D 1521 's Advantages
Released 5 years and 3 months late
Higher specification of memory (4 vs 3)
Newer PCIe version (3 vs 2)
More modern manufacturing process (14nm vs 32nm)
Lower TDP (45W vs 130W)
Intel Xeon W3670 's Advantages
Higher base frequency (3.2GHz vs 2.4GHz)
Larger L3 cache size (12MB vs 1.5MB)