BMW has a healthy business in its own performance parts division, as evidenced by its ability to actually sell people the $4,374 M Performance exhaust. This video takes a look at the regular versions of its cars in comparison to the performance package versions through the eyes of owners on an autocross-style course.
There's no doubt that BMW's cars--especially the turbocharged ones--are readily opened up by a handful of relatively simple modifications, sometimes as simple as an ECU flash. The question is, are those ugprades worth the price of entry? According to these owners, the answer appears to be yes.