Choosing Penn with the assumption that you will do well and get into Perelman is a mistake, in my opinion. They have hundreds and hundreds of premeds every year and only accept a couple dozen of their own into the MD cohort. You'd be much more likely to have to go elsewhere than to remain. In fact, given the significant weedout of the premed process and the caliber of students at Ivies, you are probably more likely to drop off the track altogether than you are to matriculate to Perelman.
Building a top-tier medical application can be a real pain in the ass. I did it, and can tell you firsthand that college would have been so, so chillaxed if I didn't have to care about an A vs A- or spend hundreds of hours on ECs. Plus all the expense, time, and stress of the MD application cycle.
Don't get me wrong, I'm not a huge fan of BS/MD programs, because I think they lock you into medicine too young. If you know you want to be a physician they can be a golden opportunity, but if you are just defaulting to premed because that seems to be what most smart Asian kids go into? Then I might hesitate. As the above poster said, if you were to change your mind and want to do something like finance, consulting, VC, a PhD, or any other career than medicine, then Penn will be a better launchpad into your first job.