The most common misconception about BBK is that they increase braking power. They do not unless they are designed to increase bias to the front. Increased thermal capacity by using larger calipers, rotors, and pads is the reason.
Therefore, unless you track your car, there is absolutely no reason to waste any money. Well, I guess you can spend the money if you absolutely have to have them for aesthetic reasons.
This is a good read:
http://www.cquence.net/blog/big-brak...-do-they-work/