R-60 through R-100 - Is it possible?
You very well may already know this, but I'm not very familiar with the regular poster's names yet. The R-value scale can be quite misleading. The number has to do with a percentage of airflow that gets through, but it's not how most people would think. R40 isn't twice as efficient as R20. R5 means that 1/5 (20%) gets through. R20 means 1/20 (5%) gets through. R49 means 1/49 (2%) gets through. This means there's diminishing returns. I'm sure you could achieve R100, but that just means that 1/100 (1%) gets through. Not a real difference there, especially considering the cost.
Once you hit R49, you've taken 100% getting through down to 2%. Getting down to 1% from there isn't going to make a noticeable difference in heating cost or comfort of the home. (Technically you aren't starting with 100% getting through with no insulation, because sheetrock/drywall provides some R value... but the point remains)
Many people consider the R-value to be overblown, and believe that properly air sealing while maintaining proper attic ventilation is more important.
I can't say these next numbers are dead on, but I'm pretty sure you're better off having a properly air sealed R20 attic than an unsealed R49 attic, because air just finds a way around the insulation generally, if it's not air sealed.