So I'd heard the supposed stats that most women are wearing the wrong size bra, and recently I came across an online size calculator at Butterfly Collection and bought some of the recommended bras. Two of them do fit pretty well and they are one band size down and two cup sizes up (!) than my previous size.
Given that cup sizes above D aren't very common in stores, if you're a busty gal do you have an online source that you really like? The ability to return seems key (I liked Butterfly Collection in general but they don't allow returns on anything that's on discount sale, which is not so helpful - but they are in Canada, FYI, if any Canadians are looking for a nice source, and they have free shipping to the US and Canada.)
[Side note: switching from a wirefree to an underwire bra is taking some adjustment - is it just me?]