Intel Core i5 8259U 's Advantages
Better graphics card performance
Lower TDP (28W vs 45W)
Intel Core i5 8400H 's Advantages
Higher specification of memory (DDR4-2666 vs DDR4-2400)
Larger memory bandwidth (41.8GB/s vs 37.5GB/s)
Higher base frequency (2.5GHz vs 2.3GHz)
Larger L3 cache size (8MB vs 6MB)