Mesh networks are based on Wireless Mesh Routers (WMRs) that interconnect themselves to form a wireless back-haul able to route traffic from/to end-users. The behavior of radio interfaces used by WMRs has a deep impact on network performance. Various recent wireless technologies are able to perform transmission at multiple different rates, depending on channel condition. How to effectively use this new multi-rate enhancement, in multi-hop mesh networks, is still an open issue. In this paper we present a simulation case study that highlights the impact of different rate-adaptation mechanisms, at Transport layer, in terms of throughput and end-to-end delay. In particular we compare MAC-embedded rate adaptation mechanism vs. rate-aware routing and how they behave in both congested and not congested networks. Results lead us to argue that using of shorter high rate links does not degrade end-to-end delay, even in congested condition, while preserving throughput capacity.