Tim, I will be applying the exterior boards first, and then infilling from within as I am living in the cellar hole below the frame and want to get things enclosed (tarps for walls currently). So render is not really an option. Having the mass on the inside may be advantageous. However, consider that either way, the dew point could likely occur at the interface between the woodchip clay and the cellulose. I fear moisture buildup in the cellulose directly behind wood siding, while the woodchip clay packed tightly against the siding would seem to mitigate any moisture issues, and eliminate the need for a vapor barrier or drainage plane. By the way, siding is to be vertical kiln dried pine shiplap boards (8") with batten strips over the joints for double coverage.
As to the performance of woodchip clay, I know people in New Hampshire with a straw clay house, and they think it quite efficient. I suppose it depends a lot on the size of the woodchips and a bit on the species of wood. R-values for softwood are ~1.25 per inch for solid wood, so a 12" wall would be ***at least*** r-15. Sawdust probably approaches cellulose in r-value (since it is basically cellulose and lignin) which is in the neighborhood of r-3.

Mike, I have a 1' cavity to fill, and was talking about using 6" of woodchip clay and 6" of cellulose. I mentioned 2x2 studs to hold lath and plaster for the finished interior wall.