I can definitely see that some more information can be useful, so here are some clarifications:
The clients are robots, receiving commands from a central server at irregular intervals. Peak will be around one message per three seconds.
The clients sends updates on their status to the server, this is the referred 1-7 messages per second, and by far the majority of the traffic.
In idle state they will send one message per second as an "isalive" message, while working they will send more often, up to 7 per second.
There will never be any communication between clients, everything goes to and from the server.
The timing constraints are that 50% of the messages should arrive within 100 ms, and 99% within 500 ms.
So any topology that can satisfy these constraints are a viable solution.
Advertisement channels sounded promising! I'l take a closer look at that!