I've been umming and aaaing every day over mine. I'm a 10 with a large chest and got the 12. I'm a bit worried about it getting bigger but I think PNGirl's post has convinced me to keep it - the link you posted is such a great look! I already have one lighter leather jacket which is much smaller but I think I'll keep it for wearing over summer dresses. This one is heavier and better for winter I think.
This one is also fairly snug over my hips when zipped and I hate it when leather jackets are too small there and bunch up at the waist. A 10 would probably be too small when closed.
If I'm feeling brave I might post some photos and submit to the MN fashionistas' advice!