The Intel Core i9-14900 is the objective winner of this comparison, securing victory in nine out of fourteen measured specifications. Its most significant technical advantage over the Intel Core i5-8400 is its L2 cache, which is 2033% larger. While the Intel Core i5-8400 maintains a 70% advantage in Max Turbo Power, the superior cache capacity of the Intel Core i9-14900 establishes it as the more capable component across the majority of the evaluated metrics.

Users prioritizing high-end technical specifications and the massive cache capacity provided by the Intel Core i9-14900 should choose it for their builds. Conversely, the Intel Core i5-8400 remains a viable option for those who specifically require the efficiency profile associated with its 70% better Max Turbo Power rating. Selecting between these two processors depends on whether your primary requirement is the expanded cache architecture of the newer model or the power-related advantage of the older unit.