Intel Core i7 6700K 's Advantages
Integrated graphics card
Higher base frequency (4.0GHz vs 3.8GHz)
Lower TDP (91W vs 165W)
Intel Core i7 9800X 's Advantages
Released 3 years and 2 months late
Higher specification of memory (DDR4-2666 vs DDR4-2133)
Larger memory bandwidth (79.47GB/s vs 34.1GB/s)
Larger L3 cache size (17MB vs 8MB)