Thanks for the education. So, the highest return solution for me is a fresh layer of Tyvek over the cdx, enough foam in the stud bays to make it airtight and then whatever is cheapest to fill the bays? Probably something like 2" of foam and then R-11 batts? That is likely going to be true for my attic floor as well? I have 14" steel on 2' centers underneath the old flat roof. Then, as much room on top as I choose to use on top of the old roof deck. I could do 2" of foam to seal the old deck. 12" batts underneath and then 12" of blown-in on top? Gets me somewhere in the R70 range? This is a long term investment for me, so it can be amortized over 50 years even if it does not improve the value of the house at all. The dollars saved are a bit hard to measure because my wood is currently largely free. But I imagine that gathering and processing firewood isn't going to get any easier as time goes on and someday we may be prohibited from burning and forced to buy from an energy company anyway.