This study investigates grinding media behavior and grinding efficiency in a laboratory-scale ball mill under different rotation speeds to identify energy-efficient operating conditions in ball mill grinding operations. Grinding efficiency is evaluated in terms of the effectiveness of energy transfer into particle breakage, as quantified by PBM-derived breakage-rate characteristics, rather than by conventional metrics based solely on energy consumption. Batch grinding tests were conducted at several fractions of the critical speed, and a Population Balance Model (PBM) was calibrated for each operating condition to quantify the corresponding breakage-rate characteristics. In parallel, Discrete Element Method (DEM) simulations were performed to analyze the motion of grinding media as a function of rotation speed. Media motion descriptors derived from DEM were integrated with the PBM-based breakage parameters to interpret efficiency trends. The results show that grinding efficiency does not increase monotonically with rotation speed; instead, an optimal operating region exists within the investigated range due to the balance between impact-dominated and surface-contact-dominated motion regimes. By linking DEM-quantified media behavior indicators with PBM-derived breakage-rate coefficients, the proposed integrated framework enables physics-based estimation of the optimal rotation speed region. This methodology provides a transferable basis for analyzing and improving grinding efficiency in ball mill grinding operations.