Departed 1998 SL500 (and the Pano is in Bogota)
Anything done to increase the 'exposed' surface area of the disk rotor will help cooling. So drilling gave the most surface area but also weaken the disk (slightly). Dimple also increase the surface exposed to air and it does not weaken the disk. Slotted disk provide channels for water to 'spin' out, and also increase the surface area.