Rules of Thumb:
For systems where there are 100 concurrent users and/or large and long running report actions are common, it is recommended to use at least 32 threads, in each DRAS task.
To determine the number of concurrent users, turn Message Suppression OFF, and review the CA DRAS task log for the high number in the “conid(nn)” messages.
If the conid high numbers are close to the Threads setting, then Threads should be further increased.
See KB000070331 for another "Threads" discussion.