David, I'm one of Kathie's partners and let me add my thoughts to your dialogue. You said the answer to "how big?" was some version of "it depends" but, you asked, depends on what? In our work, the first question seems to be around what is the business reason for seeking alignment of the people of this organization. The answer to who needs to be in the room and what they need to be talking about really sets the parameters of the discussion. The rest is logistics. When Kathie said there must be some organizing principle that unites people, it is usually around what they yearn to create together. So, if a division or a geographical region act like a complete system for some purposes, they can get together and work toward becoming one brain and one heart around that issue.
If an entire organization needs to be aligned then it follows that the conversation that must take place will need to involve everyone in some fashion. Chopping up the organization w