The Layered System Generator is used to create synthetic distributed systems of tasks with client-server style (RPC) interactions, representing a wide range of software architectures and workload patterns. A synthetic task system can be used to generate network and workstation traffic which represents the load from a planned software system, so one can observe its probable performance when run on the target network, or its probable impact on other existing applications. It can be used to evaluate the planned software design, or the target network's capability, or both combined. Using LSG, tests were made with systems of up to 39 tasks on a UNIX network, to investigate the performance changes that occur when a small task system is scaled up in size. The performance recorded across the range of experiments was also compared with predictions made by an analytic performance model. The errors were found to be small provided an allowance is made for workstation daemons and similar load components.