One challenge of composite Web service architectures is the guarantee of the Quality of Service (QoS). Performance evaluation of these architectures is essential but complex due to synchronizations inside the orchestration of services. We propose methods to automatically derive from the original model a family of bounding models for the composite Web response time. These models allow to find the appropriate trade-off between accuracy of the bounds and the computational complexity. The numerical results show the interest of our approach w.r.t. complexity and accuracy of the response time bounds.