Upgrading to a BBK should be towards the bottom of the upgrade list. The fastest drivers in my region don't run anything beyond the stock caliper/hub setup.
Just get some good pads/rotors, and you'll be fine. FWIW I run Hawk HP+ with centric rotors front, OEM level shoes in the rear. Plenty of stopping with a ton of dust and noise :D
Parking Lot Hero
2008 WRX daily driver
2003 ZX3 23D Autox Car 42 FSP
"Hella Functional - Raced, Not Hard Parked"