Thanks all for comments so far. I guess I phrased the question in a way that seemed to steer towards one model versus and the pros and cons of each. Kristin Connell thanks - yet more support for the fact that we should consider becoming a Sirius client!
I know I saw some research that indicated that were an organisation has a centre of competence higher campaign success and better metrics resulted becuase of the wide visibility of what works, and the deep experience across an organisation that a central team can have, and which is very difficult for a hybrid or federated team to have. Guess I will have to keep searching the web and post back here if I find those results.
Greg