[Zope] Object DB Capacity

We are currently in the process of building a site with Zope that we anticipate will have a large object database. We have some concerns about scalability as the database continues to grow. What is the maximum capacity of the Zope object database? At what point does performance begin to degrade? Is it possible to have multiple Zope servers, each with a subset of objects, working together to "load balance"? How about multiple object databases on one zope installation? Any help would be appreciated.