Size 4 - chest = 36", waist = 36.5", hip = 41"
Size 6 - chest = 37", waist = 37.5", hip = 42"
The neckline is where I could really tell that it was a little big. Under the arm it doesn't look too big. The under arm area has been an issue in some of the J Crew pieces this year. Not so much in this dress, which is good.
If I could re-do this pic, I'd give it a thumbs up. The fabric is beautiful and the dress looks great in the right size. I've since tried the size 4 and it was much better. Take the smaller of your two J Crew dress sizes if you are in between.
I also tried on the café capri in gilded dot brocade.