I have seen hundreds of projects in last 6 years and I can say that quantity of the team doesn't mean anything. there are teams consists of 5 people and they do better than team of 50 people. So quality is more important than quantity.
Quality over quantity I would say that can be applied in many things in our life and same goes for dev/project teams. I think a project cannot be "quantified" by the number of persons it has working on it, well, obviously more people can perform more tasks but if they are a bad team they will accomplish the same either they have 30 or 3.