Multi-Channel Multi-Interface (MCMI) Wireless Mesh Networks spread the load across orthogonal channels to improve network capacity. However, due to the limited number of available orthogonal channels in the radio spectrum (3 in IEEE 802.11b/g and 12 in IEEE 802.11a), interference and contention are still major factors in such networks. Then, an efficient channel assignment scheme is required to enhance the overall throughput. In this paper, we present three models to evaluate network capacity associated to any channel assignment strategy. These models permit also to extract what we could obtain with an optimal centralized assignment, constituting an upper bound. We present extensive numerical and simulations results, taking into account realistically MAC and routing aspects. In particular, we investigated the impact of the channel assignment strategy onto IEEE 802.11s, and presented modifications that may improve its performance.