A good architecture is a necessary condition to guarantee that the expected levels of performance, availability, fault tolerance, and scalability are achieved by the implemented system. While in the software architecture domain several approaches focus on checking static characteristics of software systems, a general approach to performance analysis, independent from a specific application domain, is still missing. In this paper we focus on the analysis of performances of an event-based middleware with two objectives in mind: first, to determine the design alternative that provides the best performances; second, to experience with statistical analysis and simulation tools in order to understand their applicability to the evaluation of software architectures.