edmunds.com is a good site also - I'm not sure how well they cover new car pricing, but their TMV (true market value) is a pretty handy figure when buying CPO (doesn't do you much good) .. Although it doesn't matter much when one is buying a 330 convertible - dealers know someone will buy it, especially this time of year.
If you get 5-7k off the sticker, you should be thrilled. I was thinking more like 2-3K - wait until sept-oct and you'll probably do better though.