The Intel Core i9-14900KS is the objective winner of this comparison, securing victory in ten out of fourteen measured specifications. Its most significant technical advantage is its L2 cache, which is 2033% larger than that of the Intel Core i5-8400. While the latter component holds a 74% advantage in Max Turbo Power, the superior cache capacity and overall spec count establish the former as the more capable processor across the majority of evaluated categories.

Users requiring maximum cache capacity for intensive computing tasks should choose the Intel Core i9-14900KS to leverage its substantial architectural lead. Conversely, the Intel Core i5-8400 remains the appropriate selection for those prioritizing the specific power efficiency profile defined by its Max Turbo Power advantage. Selecting between these two processors depends entirely on whether your primary requirement is the expansive cache performance of the newer model or the power characteristics of the older unit.