Intel Core i3 7100 's Advantages
Better graphics card performance
Higher specification of memory (DDR4-400 vs DDR4-2666)
Higher base frequency (3.9GHz vs 2.8GHz)
Lower TDP (51W vs 65W)
Intel Core i5 8400 's Advantages
Released 9 months late
Larger memory bandwidth (41.6GB/s vs 35.76GB/s)
Larger L3 cache size (9MB vs 3MB)