853 is an oversized tube set, so it will be noticeably stiffer in the bottom bracket and lighter. Also, there is a slight aesthetic difference in tubing diameter which some ultra retro-grouches tend to hark on.

Really it depends on the use. If you're a masher, enjoy sprints, steep out of the saddle climbs or are fairly weight conscious I'd go for the 853.

If you really like the feel of old 531 frames, may as well get what you know in the size and colors you want. Also, don't let the 531 rear stop you from getting the curvey stays, if you like the look don't worry about it.