Just received my order of 12 and 16 awg of that silver plated wire. 12 awg looks like 14 awg because the teflon insulation is thin and the 16 awg looks more like t-stat wire. As a better dielectric than PE, it doesn't have to be as thick, I guess. Not talking high voltage anyway but we are talking low capacitance. It's also fairly stiff. Still flexible but nothing rubbery about it. Doesn't fray when insulation stripped either.
On the stuff you ordered, you did notice that was 10 awg combined, right? Meaning that each wire of the twisted pair is closer to 13 awg.