The Intel Core Ultra 5 245K is the objective winner of this comparison, securing victories in eleven out of fourteen measured specifications. While the Intel Core i5-8400 maintains a 59% advantage in Max Turbo Power, the newer processor dominates in cache architecture. The most significant performance differentiator is the L2 Cache capacity, where the Intel Core Ultra 5 245K provides a 1633% advantage over the Intel Core i5-8400, representing the most impactful technical improvement between these two components.

Users prioritizing modern architecture and significantly expanded cache resources should select the Intel Core Ultra 5 245K for their build. Conversely, the Intel Core i5-8400 remains a viable option for those specifically seeking the power profile defined by its superior Max Turbo Power rating. Choosing between these parts depends on whether your requirements favor the massive L2 Cache capacity of the newer model or the specific power characteristics offered by the older unit.