i am looking forward to see how your show stopper turns out! I got half way through making this one and realised that my usual supply of wide spirals werent right for the job, and this corset has become a ufo :( I ended up drawing the pattern up by hand using the scale adn found it turned out to be around a Newzealand size 10/12, but I havent made any other sizes either. Id love to make this into an underbust, and im sure i will be inspired to finish mine after seeing yours!
I know the other people I know who have made this say it ended up a size UK12, but this enlarged to be a small UK 10 for me (I don't know if its because I took a picture of the pattern on my cell phone, uploaded that onto my computer and enlarged from that, as the image may have ended up ever so slightly distorted or something - I will see what happens if I do it properly and scan the image in rather than doing it the lazy way with a camera phone) The back panel certainly ended up just a tad too narrow for the two steels, and I had to add the extra height to the pattern, so it would seem something happened.
I hope you do finish your version, it's a wonderful corset :)