Re: Insulate Garage
Keeping a garage warm is nearly impossible because of air leakage around the garage door and the heat sink created by the concrete slab and the foundation.
Since insulating the former is impossible and insulating the latter is prohibitively costly, what ever insulating you do will be a ?feel good? exercise.
A better use of insulation is to maximize R values around the heated envelope.
A heated house loses heat in several ways:
25% - Attic
35% - Walls
15% - Floors
15% - Drafts
10% - Windows
Attack those areas with the greatest payback first. I would be careful about making the home to tight. Some air exchange is good.
Not to hijack a thread here, but I disagree with the window percentage -- unless it's in view of the whole house vs. windows (you probably have a little more wall space than you do windows

)
Windows come standard with a u-factor rating. Without getting too technical, they're the reciprocal of the R-value. For instance: a window with a u-factor of .34 = roughly a R-3. Some of the BEST windows I've ever seen are around a .25 rating which translates into an R-4.
Sidewall insulation for 6" walls are typically an R-19, or R-21. However, in real world practices (rather than laboratories), you're lucky if you get better than an R-15. Either way, an R-15 is better than an R-3.
I'm also thinking that the heat loss for the attic is dependent upon the amount of insulation (as is ALL of the numbers you posted) that is existing in the attic. I'm guessing that an attic with 6" of insulation is going to lose more heat, faster than an attic with 12 or 18".