Not trying to make fun of you, but a little research and higher- proper
R value and proper supports can save you alot more than your ISP
connection every month. Insulation is cheap, and the attic is the best
place to start since heat rises. In walls you are limited to 3.5" so
not much you can do. Drywall has no seams when finished , so less air
infiltration, plus no dust to fall on you and make you itch. Drywall= R
1 apx and shouldnt be used as a total R figure. Ceiling tile with the
seams allow for too much air to pass to be considered alone an R factor.
Check out Dow, Owens Corning, Celotex, Energy Star, EPA, and other Gov
sites that publish complete info on insulation, Zones, and all you need
to know on efficiency and insulation.