When you have a minute, I'd love to hear more about the differences in finish/quality.
I got a good ride in this morning and I think it rides a bit smoother than the Waltly and takes out a bit more of the harsh trail buzz. Could also be placebo it's hard to tell but I think the double butting gives a better trail feel.
The finishing on the frame is a bit rougher than the Waltly, for instance there was a small notch inside the head tube that needed filing down (maybe half a mm). Nothing huge just not quite as polished, like there isn't that last person that goes over the finished frame and gives it the last touches. Nothing that impacts the quality but small details.
Now the big things:
The cranks on the Waltly never spun more than 1 rotation even with the chain off in the work stand. The XT bottom brackets aren't the loosest but I always suspected the bottom bracket shell was ever so slightly misaligned. The XACD frame I get 3 or 4 rotations of the cranks with the chain off in the work stand so it looks like the bottom bracket shell is better aligned.
The seat tube on the Waltly alway irritated me because it had to be torqued way over spec to stop the seat post from spinning. I suspect, and others here have eluded to, it being slightly ovalised and not being reamed properly. The XACD frame doesn't have this problem the dropper is in and done up (quick release seat clamp so can't test torque) with minimal ugga duggas and it holds nice and firm.
These are the two things I have noticed so far and I think it shows a higher level of engineering but less focus on ascetics, this also meshes with the two companies slightly different approaches to customer service.