Stuff went super slowly again as states happened (everything went well) and I dithered around trying to fix the feather patterning (including readjusting a lot of the feathers that got displaced and put everything else out of whack when I fixed the underlying mesh, I really should know better by now that while other people can get away with not doing things I never can) and flatten things out a little bit.
And after spending way too much time and effort on this malarky and really struggling with polydown, I revisited the idea of particle down. The last time I tried this it didn't work out great.