The main difference at first glance is that the four Fashion sized ladies have smaller heads, more in proportion to a real woman. The three ladies on the outside are proportioned like standard MSD dolls. Miho's Athletic FID body is slightly larger than everyone else. Grace's Slim FID and Monica's Raccoon bodies are very close in size, although Monica has a slimmer neck. Naomi's SartoriaJ 45 Aphrodite body has a slightly smaller upper torso than the other ladies, but much bigger hips and thighs. JID Asa has the same size upper torso as Grace and Monica, whereas Narae and Lily are much slimmer.
Since I make all my own doll costumes, I always make the Fashion size outfits to fit the Iplehouse Slim FID body, and with adjustable lacing, so any one of the ladies can wear them. Both Narae and Lily's default outfits were originally made to fit an Iplehouse JID, and it turned out that they will now also fit the Fashion ladies.