The need to bring high-quality systems to market at ever increasing pace is driving the use of system-level models early in the design process. This paper presents a new unified modeling framework, called the extended queuing Petri net (EQPN), which combines extended stochastic Petri net and G/M/1 queuing models, to realize the design of reliable systems during the design time, while improving the accuracy and robustness of power optimization for high-speed scalable networking systems. The EQPN model is employed to represent the performance behaviors and to minimize energy consumption of the system under performance constraints through mathematical programming formulations. Being able to model the system with the EQPN would enable the users to accomplish the design of reliable and optimized system at the beginning of design cycle. The proposed system model is compared with existing stochastic models under real simulation data. Experimental results demonstrate the effectiveness of the modeling framework and show that our proposed energy optimization techniques ensure robust system-wide energy savings under tight performance constraints.