Im kinda eating my own shirt here but i asked a very similar question last week
I track my car and currently run a M sport drilled slotted rotor with M sport pads. I upgraded the system to stainless steel lines and hi temp fluid. On the track i get a few really hot laps in before i see break fade where as on the stock factory ones i got 2 maybe 3 laps in MAX before the car was dangerously out of control from loss of breaking.
Last week i asked about going to a BBK or what thoughts were and it was obvious i didint do enough of my own research.
In the end i agree with the above and it comes down to what your doing with your car. If your staying on the street and just having fun with the power at the odd light or highway pull, the factory calipers are 100% more then anything you need.... what your running is fine IMO... upgrade your rotors and pads and go to hi temp fluid (prob $500 to do this to the whole car pending the brand you go with)
If your actually hitting road race events or possible autocross then you should possiblty consider looking at new calipers, but even at that, you still have wiggle room with pads and rotors or even a break vent kit from stillen....
Going BBK is expensive... totaly worth it if you need it, but for the cost i just dont see the value untill im pushing the car so hard that its a needed upgraded to stay on the track...
Before you consider changing your calipers or spending $5K going BBK, try experimenting with diffrent pads (hawk HP + or Stop Tech Sport edition) and see how you like the feel.