I agree with John, its dangerous to try and drill out your rotors,
they're already thin enough. Remember, *true* and *proper*
cross-drilled are cast into the rotor. Drilling only creates stress
risers and will weaken the disc.
If you want the proper "factory" upgrade, and don't want to spend the
big bucks for a Movit or Brembo kit, get yourself a set of E32 750
calipers and rotors up front; E34 540i calipers and rotors in the rear.
You should be able to find the calipers cheap at any junkyard.
The beauty of this setup is your consumables - rotors and pads, are
basically standard BMW stuff that can be bought OE from any dealership
or OEM through any parts store, e.g., BMA parts as great prices.
Further, the bigger brakes are vented for more cooling.
Note - you may need to upgrade to 16" wheels, but since your car came
with those obsolete metric TRX tires and wheels, you'll probably need
to replace them anyways, if you haven't already done so. Good Luck!