I'm 5'2", 32c, 28 inch waist. I pretty much always wear a size 2, 4P or XS in JCrew shirts. (They size petites smaller, so bust and waist measurements for size 2 equal those of a 4P). That includes 2 linen shirts from a couple of years ago.
I wear the same size in the perfect shirt and the everyday. In my experience the everday is less fitted, but not oversized.
HTH.