[Zope] Active Zope threads and connection cache size

Does the size of the connection cache need to grow when Zope runs more threads. I currently am running 8 threads (default 4). I note that the current OODB connection cache size is FIXED at 7. Do I need to increase the size? I would have guessed the connection cache should be somewhat larger than the number of threads and that it should be set dynamically. Can anyone hazard a guess as to what it should be? twice the number of threads? more? I am running Zope 2.6.3b2 but I think the same question is relevant for all versions of Zope.