Improving the energy efficiency of large grinding mills is of great importance to reduce the energy cost of mineral processing. The ratio of SAG mill to ball mill’s energy consumption varies greatly among SABC operations. Thus far, very few research studies have been conducted to demonstrate how the SAG mill or ball mill responses to the change of circuit energy distribution in terms of comminution efficiency. The present study investigated the energy performance of an operating SABC circuit at variable circuit energy distributions. An energy benchmarking model was used to assess the comminution energy efficiency of SAG mill, ball mill, and overall circuit. It is found that the target SABC circuit achieves the highest overall energy efficiency when 37.6% of the total circuit energy is distributed to the SAG mill and 62.4% to the ball mill. The maximum energy efficiency of this SABC circuit is approximately 25% when compared to the minimum practical energy required to carry out an equivalent comminution duty. The study also showed that the ball mill is more sensitive to the variation in circuit energy distribution than the SAG mill.