You need to look back at Post #2 above or click on this link:
http://www.300cforums.com/forums/109345-post2.html
Repeat after me: Rotors that have been slotted
AND drilled are bad!
If a vendor is clueless enough to drill
and slot rotors, then you can be reasonably certain they don't know the proper drilling or slotting patterns to apply to maximize the benefits while avoiding structural damage to the rotors. And no,
more holes and slots is not better than fewer holes and slots! You want the hole pattern to be such that the entire surface of the pad is swept by them. To do this, you need the holes in adjacent rows to be staggered. You also need to space the holes appropriately, such that they don't cut into any internal cooling vanes. And you don't want the size of the holes to exceed 4mm in diameter.
Here's an example of drilled rotors done properly:
Note that the spiral "arms" of the drill pattern can run in the same direction or the opposite direction of the internal cooling vanes. It is critical for the spacing of holes to not hit or come too close to the internal vanes. You can see this in the cut-away photo above.
Slotted rotors should be cut in a direction opposite to the internal vanes so that each slot is supported by several vanes, which act as reinforcement. You should NEVER slot the rotor in the same direction as the internal vanes, since this dramatically weakens the rotor. Since the vanes should lean toward the back of the car at the top of the rotors, the slots should tilt forward in the opposite direction. The slots should never be machined all the way to the outside edge of the rotor. If they do, the rotor can crack under heavy use.