I got some interior feedback from Tesla -- any errors are mine.
(1) The 'microfiber' on the Standard is indeed mostly polyester (it's a blend). Even if you get leather seats on the Standard, there will be microfiber on the doors and dash and perhaps elsewhere.
(2) The Signature will not have any microfiber. Most of it will be Nappa leather, but some high-wear areas will be a 'synthetic leather' which is actually cotton.
The seat interiors are not certain, but my 'customer advocate' thinks they're going to be foam (which would mean, not polyester). No information about the headliner or carpeting or trunk carpeting yet -- these are the only remaining parts of the Signature which might have polyester.
Accordingly, given my polyester allergies, the Signature is definitely preferable. It comes out to a $5550 - $7050 premium for me (depending on whether I consider the pearl white paint worth anything), but that's probably approximately what it would cost to replace the microfiber in the Standard, so it's a good deal.
So I finally voted in the poll. Pearl White Signature with white leather interior and banana leaf accents, and aero wheels, here we come.... (I'll never use Performance, I'm just not that sort of driver.)