Anyway, it sounds like you are contradicting yourself a little - above you say size 14 at 5'3" is obese, yet size 12 at 5'5" is healthy?!
As a matter of interest, (Fobs & cahir) how tall would a woman have to be to look OK as a size 16 in your opinion?
Edit: oh - number one Dave...obviously.
A size 14 on me (5'3") would look obese. On some other women of my height it might just look overweight. It all depends on body shape. I think you'd have to be quite tall and broad to carry off a size 16.
Shop sizes are funny anyway. In Topshop I'm a 10, Oasis an 8, Gap a 6 (US size 2 - serious case of vanity sizing there).