IMO OP, unless your hard core tracking your ///M, it's not worth spending $5,6 or 7K+ on a BBK. They look awesome and I have APracing brakes that look amazing compared to the stock and for occasional tracking and mainly spirited mountain driving their great but an overkill. I know a professional driver here in the SW that runs a track modded M3 all over the South West and west coast, kicks everyone's ass including Porsches and the few Ferrari's in this area of NM. Holds the fastest track times at Deming Speed way (since I last heard). He runs with stock brakes and racing pads and racing brake fluid for the obvious reasons. He mentioned to me that with just those brake mods, he can run for laps after laps and he doesn't get much brake fading and the OEM system has the thermal capacity BBK have.
Anyway, if you got the $$$ to blow, go for it, it'll look awesome and performe just the same. But the M3 stock brakes with racing brake fluid and appropriate pads will be more than adaquate.
Your choice of course.