Your building envelope is the most important part of your home when it comes to energy efficiency.  R-value while important is not the end all be all. The most overlooked element in the homes envelope is air infiltration. The DOE says that up to 40% of your heating and cooling energy is lost as a function of air infiltration. An effective air barrier that reduces or eliminates the air infiltration is a key component to your insulation plan.  Using alternative insulations like cellulose and spray foam can make a huge improvement in your homes efficiency when compared to fiberglass batts, even given the same r-value. Spray-in insulation can fill in all the little spaces that traditional batt insulation can't.