Some time ago I wrote to PG about this very subject:

Paul Graham wrote: | Thanks, John. Dunbar's number is more about the size of societies than | the size of a group that can cooperate to complete a task. There the number | is more like 8-12, which I believe prob corresponds to the smallest unit | in an army.

Not sure the army is the best analogy since they operate with large amounts of funding and not the same restraints as a start up. Terror organizations are a better analogy since they have to combine team effectiveness with minimal size (for security and finance reasons). This seems a lot like a start up that needs an effective team of the smallest size (for mostly finance reasons).

For example, the IRA was divided into 6 to 8 man operational units.