Performance assessment and optimisation for MPC have attracted much research interest. As a typical performance assessment benchmark, the LQG benchmark is regressed from asymmetrical points, leading to unnecessary computation and unsatisfactory regression results. To tackle this problem, an equigrid LQG benchmark was proposed for the two-layer MPC assessment and optimisation, and the optimal setpoint for MPC was calculated to replace the experiential one. Then the LQG benchmark for sensitivity analysis was introduced. Economic performance assessment of the control system in a delayed coking furnace shows the effectiveness of the proposed approach. (c) 2012 Canadian Society for Chemical Engineering