[Zope] ZODB 7 thread limit?

Hi there, I was just wondering if any one can explain the reasons for the 'pool_size=7' and 'version_pool_size=3' numbers which are part of the defaults for the ZODB (lib/python/ZODB/DB.py)? Is there something behind the magic numbers, or should I change them only at great risk to myself and my Zope installation? I'd like to raise the number of threads active on my site above the 7 limit... Searching for ZODB wisdom-ly yours, --Brian Hooper