A year later and I'm still happily using the same phones I decided to keep out of the AKG collection. Today I finally repaired the set of K401 drivers I had sitting around for a couple years and swapped the drivers and baffles into my K400... I think I prefer the sound this way (not as good as regular K400 for certain music, but less sensitive to bad recordings so I can use it more often). This means I technically have a K401 now, putting me back at my initial choices before I started second-guessing myself.
I still miss the other AKGs sometimes, but it seems I made the right choices for which ones to keep.