The Figures are in:

The cavities have a total r-value of around r-18, actually slightly higher because I did not figure the value of the clay and plaster, and rounded down. This is the combined r-value of the foam board, 3/4" outer planking, and 1-1/2" inner planking

7" thick posts have an r-value of about r-8, slightly more for most softwoods, slightly less for hardwood.

I figured that the cavity generally occupies about 88% of the surface area of the wall, and the frame about 12%. For more complicated framing the frame may occupy as much as 20% of the wall area. 20% frame gives an average r-value of 15.5, 12% frame gives an r-value of 16.5. This is every bit as good as a 2x6 wall with no exterior foam insulation.

here is the formula I used:

a= average r-value
f= r-value of the frame
c= r-value of the cavity
The wall is divided into 20 sections, with each portion given its proportion of the 20, so the frame has 5/20ths of the wall area if it is 20% and the cavity would be 15/20ths

a=(5f+15c)/20, a=(5x8+15x18)/20, a=15.5
or
a=(3f+17c)/20, a=(3x8+17x18)/20, a=16.5

Not a super home by any means, but nonetheless a more than adequate insulator. Certainly meeting the prevailing standards.