Intel Core i5 6400 's Advantages
Lower TDP (65W vs 125W)
Intel Core i5 12600K 's Advantages
Released 6 years and 1 months late
Higher specification of memory (DDR5-4800 vs DDR4-2133)
Larger memory bandwidth (76.8GB/s vs 34.1GB/s)
Newer PCIe version (5.0 vs 3.0)
Higher base frequency (3.7GHz vs 2.7GHz)
Larger L3 cache size (20MB vs 6MB)
More modern manufacturing process (10nm vs 14nm)