Well, thanks to some great advice from the commenters on this blog and to my posts at PatternReview and SewLisette I think I'm making progress. I narrowed the shoulder by 1/2 an inch. I took up an inch in length above the waist.
I've also got an old sheet all picked out with which to muslin this shirt again. This time I'll try the size 12 with an FBA. (My high bust is a 34 and my full bust is a 38.) Then and ONLY THEN, dear readers, will I know for sure which size is better for me, the 12 or the 14. ;)