Understanding the spread of information on complex networks is a key issue from a theoretical and applied perspective. Despite the large effort in developing models for this phenomenon, gauging them with large-scale real-world data remains an important obstacle in the field. In this work we assess the relevance of the classic SIR model to capture key properties of spreading phenomena in real communication networks. We use a real file spreading trace in a P2P network to calibrate the model and to simulate similar diffusions. Comparing spreading cascades of real and simulated traces we observe sharp topological differences and conclude that this model fail to mimic key properties of such cascades.