Ok, today, Neo is 14lbs and an ooch, 17.5" +/- behind the arms. Remo is 12.75lbs and 16.5" behind the arms. I tried PTP's method of measuring against a wall and no success with that. They're convinced that more evil is afoot since we just finished baths and a trim, immediately sit and go small. Best estimate is 14" max for Neo and 13" max for Remo.
In the Kurgo they both wear the small. In the VelPro, the XL fits Neo best, allowing his front legs to move without rubbing, fits with room for fingers under the harness, and still can adjust a bit. The Large fits Remo, a bit more relaxed than the fit on Neo, but the Medium is definitely too small for Remo. He grew out of his original one.
Neo wears the largest of the mesh version, but has a comfort room. Remo is too big for the medium but the large is a bit loose, although it stays on with no problem.
I'm going to look at the leather style for the holidays.
The photo is not from today.