This topic comes up on the Austin food subreddit on the regular and I'll touch on your suggestions and make a few of my own. Plus I just got back from Paris and like a true Parisian, consider myself an expert and everyone else is wrong.
Sweetish Hill--I'm lame and have only been once since the remodel and don't recall it being exceptional in any way besides the how hot the lady customers were
Sour Duck--love them, although like @HenryJames I'm constantly confused how you can call yourself a bakery but run out of pastries by 10 am. Kouign Amann is the standout.
Central Market--very inconsistent. I've had to return pastries because there was butter chunks (ineffectively creamed) and a lot of times they look better than they taste, particularly out of the cake case. Not a pastry but I do appreciate they offer a $2 baguette when Whole Foods is only stocking $5 versions from easy tiger.
Upper Crust--love the morning buns but their parking lot has more helpless drivers than the Arboretum Trader Joes and being closed on Sundays is no bueno.
Quacks--always solid, but never better than that. Really their cakes are better than their pastries. Most of their staff is, errrrr....baked.
Russells--they don't get enough love, I like them better than Quacks
Epicerie--refuse to go out of pique at the subredditors that claim they have better pastries than in New Orleans.
Julie Myrtille--overrated and expensive, I don't know how you can charge $6 for a chocolate croissant that's 2 euros in Paris. I guess great for them if they can get it, but it feels like a Disneyland version of a patisserie designed to remove money from indiscriminate Gen Z.
Heaven's Bistro--for my money the most under-sung hole in the wall bakery in Austin, and the best almond croissant.