Intel Core i7 6900K 's Advantages
Higher base frequency (3.2GHz vs 2.5GHz)
Larger L3 cache size (20MB vs 18MB)
Intel Core i5 12400 's Advantages
Released 5 years and 8 months late
Integrated graphics card
Higher specification of memory (DDR5-4800 vs DDR4-2133)
Newer PCIe version (5.0 vs 3.0)
More modern manufacturing process (10nm vs 14nm)
Lower TDP (65W vs 140W)