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While interest in low-power mesh networks for the Internet of Things (IoT) has proliferated over recent years, much of the focus in this area has considered the deployment of a single sensor network, or brokering data to and from a cloudbased server. Yet, particularly for industrial use-cases such as distributed sensor-actuator networks, there is a need to consider fully-federated IoT networks where devices may be required to send data over a mesh-cloud continuum directly to devices at remote sites while adhering to strict latency and reliability requirements. To allow experimentation in such settings we present X-Lab, an open-source federated testbed infrastructure for end-to-end benchmarking of low-power wireless protocols. Using X-Lab, we establish a 4000km cross-continent setup between two sites and evaluate the endto-end performance of two low-power wireless protocols. We find that despite the large distance between sites, mesh latency often dominates the latency of the Internet–which can directly account for as little as 22% in some protocols.