Resolution:
There is no hard value for this option. It is recommended that customers try different values and then test to see what kind of performance impact the setting has. A reasonable starting point for testing is to set the server_num_threads to be the number of CPUs on the machine plus 2.  Note: Values greater than 1 will most likely decrease performance under Windows (SmartSockets 6.0r2).  Additionally it has been determined that using multiple threads is not well-suited to request/response type applications because of their fundamentally syncronous model. By our tests (done at a customer site) it has been proven that running v6.1 in single threaded mode (setopt server_num_thread 1) will provide the same level of performance as that of SmartSockets v5.2  for request/response messaging systems.
Additional Note: Even when a "sweet spot" has been found when setting the server_num_thread option changes in any  of the system variables such as increased message rate, disk I/O, increase/decrease in the number of RTserver to RTserver connections (cloud configuration) and changes in the number of RTserver to RTclient connections can influence the performance assosiated with the use of server_num_threads and re-testing is recommended.

How should I set the server_num_threads option in RTserver?