One challenge of composite Web service architectures is the guarantee of the Quality of Service (QoS). Performance evaluation of these architectures is es- sential 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-o↵ between accuracy of the bounds and the com- putational complexity. The numerical results show the interest of our approach w.r.t complexity and accuracy of the response time bounds.