When reengineering software systems, maintainers should be able to assess and compare multiple change scenarios for a given goal, so as to choose the most pertinent one. Because they implicitly consider one single working copy, revision control systems do not scale up well to perform simultaneous analyses of multiple versions of systems. We designed Orion, an interactive prototyping tool for reengineering, to simulate changes and compare their impact on multiple versions of software source code models. Our approach offers an interactive simulation of changes, reuses existing assessment tools, and has the ability to hold multiple and branching versions simultaneously in memory. Specifically, we devise an infrastructure which optimizes memory usage of multiple versions for large models. This infrastructure uses an extension of the FAMIX source code meta-model but it is not limited to source code analysis tools since it can be applied to models in general. In this paper, we validate our approach by running benchmarks on memory usage and computation time of model queries on large models. Our benchmarks show that the Orion approach scales up well in terms of memory usage, while the current implementation could be optimized to lower its computation time. We also report on two large case studies on which we applied Orion.