to ensure monthly updates, you'll need about two couriers for every 20-22 parsecs between Capital and the world where the recipient of the news is located. The cost of a couple of dozen couriers isn't much compared to the taxes of a world with pop level 8+.The theoretical noble, or group, willing to pay for his own source of information is in for an even bigger bill than he is expecting. To say a small group of ships can average J5.5 over a long distance is probably true- this does not allow for regular news.
And if the J6 courier sets off four jumps behind, it'll catch up with a J4 network in about 50 parsecs (It'll be even quicker to catch up with a network with the canonical average of the X-boats, said to be 2.6 parsecs/week).To ensure a private network can spread news of the Emperor's assassination as fast as possible, it has to have been waiting for the event. Otherwise, there is no way of guaranteeing that the monthly courier didn't leave an hour ago- making it a month before the private couriers can even send the information.
A ship on standby will equal or beat the X-boats on any distance.Even leaving ships in reserve for urgent information cannot reliably beat the xboats- either the definition of urgent is so strict the ships never actually leave, or loose enough that there is likely to be at least a day or two of delay waiting for the next ship in.
That they will, but nothing even remotely near compensating for the two-parsec difference in performance.None of this prevents private J6 ships- but they will tend to lose on turnaround time.
Hans