The Intel Core i9-14900K is the objective winner of this comparison, securing victory in ten out of fourteen measured specifications. Its most significant advantage over the Intel Core i5-8400 is its L2 cache, which is 2033% larger. While the Intel Core i5-8400 holds a 74% advantage in Max Turbo Power, the superior cache capacity of the Intel Core i9-14900K provides a more substantial technical lead across the majority of the evaluated categories.

Users prioritizing high-end technical specifications and the massive cache capacity of the Intel Core i9-14900K should choose that processor for their build. Conversely, the Intel Core i5-8400 remains the appropriate selection for those who specifically require the efficiency profile associated with its Max Turbo Power advantage. Your decision should depend on whether your primary requirement is the expanded cache architecture of the newer model or the power-related characteristics of the older unit.