EBS, Tim posted a very helpful explanation [url viewtopic.php?f=8&t=281&start=10#p2775]here[/url].
As I understand it, there is a single connection between each core and its mesh router, so the aggregate bandwidth available to the core is independent of the number of data transfers that are in progress. Since the connection between core and router is both fast and low-latency, that should not be a limitation in practice. Hopefully I haven't got the wrong end of the stick there...