Yeah drilled / slotted can be noisy under hard braking, they are about the same as standard no real performance benefit (from the ones linked to above, or any with the standard cally) other than looking pretty cool through the wheel.
For performance benefit:
1. Better pads: Mintex 1144 / DS2500 / Endless
2. Better Calipers: S3/R32/Cupra with bigger discs
3. Combo of 1 and 2
4. 4 Pots from 986 or similar
5. Proper BBK...