I did some more checking on other sites that use his method, they mention (what he didn't) is that the baffle material is 1.5", that includes the 1/4" per side used as the seam allowance, so the actual thickness for the 50F quilt is 1". Stuffed with 9oz of 850 fill.

For 1" baffle he does suggest sewing through and 6oz of 850 fill. Going with your formula this would be:

TR = 70 - (20 * 1.5) = 70 - 30 = 40F
TR = 70 - (20 *1) = 50F

So, seems like what I want is 1" sewn through with 6oz of 850.

His baffle spacing is 13" at top and bottom, 11-1/2" in between (to make the calcs easier), giving 6 chambers. The bottom 24-1/2" is tappered about 8-1/2" narrower on each side.

This sounds pretty doable for a sewing neophyte. I person I was talking with in Arizona said he made two of these and uses both when the temps drop below 45F instead of making quilts with different thicknesses. In his dry climate I can see that working, with the humidity in the NE I wasn't sure if there would be a condensation issue.

Anyone have suggestions about stuffing without a mess?