Just look at Leandro, he's got an amazing overall shape and I'm certain that it comes from his own workouts as well as his chosen eating program!
BBL is a tough program for anyone and it is very concentrated on specific 'large' muscle groups and redefining and reshaping them. In order to stick with the 'muscle confusion' that Tony Horton and Shaun T speak to, this would be a nice change from P90X to allow your body to rest from some what the workouts and find other muscles within that you haven't yet touched on.
As long as you are eating properly you will continue to gain the muscle that you are looking for. Enjoy the ride and I'd be interested to hear about your personal experiences with BBL should you choose to take the challenge

Kathleen