On a brand new bike? That's really strange.

There's a bunch of little things. Full 105 vs 105-Tiagra-offgroup-KMC, brand name vs off-brand wheels, butted vs not-butted tubing, chrome stays vs all paint, consistent vs incoherent palette.

There's a difference in how they get marketed and priced, too, one is a smaller premium bike-store brand (like maybe Soma here in the USA) with a lot of styling and high-polish catalogs with interviews of interesting people, and team sponsorships, and show bikes, etc. all designed to make you pay more to feel better about your purchase... and the other is from a sporting goods store who ordered a container full of bikes like @fietsbob said.

We went back in today and I test rode the small size which was a much better fit. So I've bought the small and we are ordering an extra small for my partner. It felt like a totally different bike and was much more nimble and easy to handle. Who knew 30mm of combined stem and top tube length would make such a large difference.

Does anyone else have experience powder coating a bicycle? Is it durable?

If well done , Yes .. its a Polyester Glazing material melted over the (scrupulously clean) Metal, at a Scorch your Pizza temperature, in an Oven.

Just curious what happened with project Audax in the end? Purchase made, and cyclists happy? I've been looking for a solid quality, steel, long-distance (53km roundtrip) commuter, that's reasonably priced and not too flashy, and these can be found in the States for ~$1300 USD on closeout, so it pretty much ticks all the boxes. Thanks!