http://www.boa-constrictors.com/Bilder/BigBoa.jpg
That's a pretty big female BCC. I like body shots of them being handled so you really get an idea of what kind of size you're looking at. I think that pic is pretty darn good at giving you an idea of what an older female BCC will be. Would you be comfortable with the snake in the pic as a pet? If so, then anything smaller would be fine as well.
There are supposed records of 14 footers that get ridiculously huge, but of all the female BCCs I've seen, I rarely have seen then break 11 foot, and even 10 footers are pretty rare.
If you're really on the fence between a female BCI and a male BCC, and aren't won over by the looks of either, I'd go with a female BCI. They've been proven to be less susceptible to imperfections in husbandry.
I personally would go with a female BCC, because I just love the look and size of BCCs. However, the GF isn't comfortable with such a large snake, so I'm limiting myself to the much lighter weight but still lengthy coastal carpet python.