I know very little about home building, but I'd do the best insulation I could afford. It will be the number one energy cost saver over the life of the home.
We do quite a few "sustainable" buildings in the commercial world...it's a lot of hooey - if you ask me. They would save more money putting double pane low-E windows, insulated doors and more insulation in the walls and roof system, than what they accomplish by going down this long list of criteria to achieve a "gold rating" with LEED or EarthCraft (solar panels, bio-retention, gray water recycling, indoor air quality monitoring, low volatile paints adhesives).
We do quite a few "sustainable" buildings in the commercial world...it's a lot of hooey - if you ask me. They would save more money putting double pane low-E windows, insulated doors and more insulation in the walls and roof system, than what they accomplish by going down this long list of criteria to achieve a "gold rating" with LEED or EarthCraft (solar panels, bio-retention, gray water recycling, indoor air quality monitoring, low volatile paints adhesives).