Great Teams Are a Mix of Old and New

To add to this nice post, I think that the composition of consistently high performing teams is that they have a set of core team members who enjoy working with each other and have worked together for long periods of time thereby developing the ability to understand how each other thinks and depending upon the project, you add new people to the mix to get a breath of fresh thinking into the project.
To take the analogy of the broadway or the movie business, you can see that most directors like to work with the same set of people when it comes to the core work like camera, editing, music, dialogues, etc and team up with new people for all other roles.
This provides them a heady balance of stability and creativity.