What's in the wall is often more important than what's on it.  Our approach with this project is a combination of blow-in cellulose at all new 2x6 wall conditions, and spray foam insulation at rim joists and existing exposed 2x4 walls.  We are also utilizing a foam Ecoseal system behind the cellulose to eliminate air infiltration.  This provides our clients with an optimum R-Value with the most cost effective approach.