How big or small should a nonprofit board be?
This is a topic frequently discussed by the "experts". I believe there is no right answer except that size needs to reflect organizational need and organizational stage of development (see my articles on stages of development here and here). On the other hand, a lot less board stress and a lot more efficiency would indeed be achieved if nonprofit boards only had 3 members (generally the legal minimum according to many state laws). But 3 members doesn't necessarily provide a lot of resources nor diversity nor guidance that can truly benefit a nonprofit.
That being said, there's a little artile in ThirdSector UK that provides some thinking about board size and how to pare down when the time comes (although there's no real insight about when that time is right).