This thread is a fantastic example of the aftermarket industry having no idea what they are selling. I've looked into the advantages of different slot designs as I will be upgrading the rotors on the P to cope with its new life on the circuit. This is what I've found or been told. 1. Brembo produce slotted rotors in a number of different combinations but always require the outermost edge of the slot to hit the pad first. This scrapes the gasses/dust out of the caliper zone and lets it exit towards the centre of the wheel instead of glogging the caliper area with dust, which can cause an excessive build up of heat in racing applications. Backing this up is the way the Brembo disks are fitted on the latest FPV range. It is as stated. 2. AP Racing produce rotors with straight and curved slots, both are required to be fitted as per the Brembo direction. 3. I rang DBA as I'm looking to use their 5000 series fronts and they told me they must be fitted as per the Brembo description. I understand this is now in contradiction to what they have told others. 4. A well known brake shop here in Perth who do a lot with the Porsche Cup racers also gave me the same description as the Brembo item. They did say however that the noise associated with running the Brembo setup could be annoying, so alot of shops fitted them round the other way so that the 'wank factor' shopper didn't come back complaining of the noise. He did say that the difference in braking performance on the street would be minimal if not undetectable, however at the track the rotors would suffer, especially if the internal veins were directional as is the case in most 'high performance' rotors. Some of the rotor producers only chasing the street market he said produced a unidirectional vein design and this mean the swapping could be done easily to suit the customer and another positive was the stock level needed to be held by the supplier. Look back at the earlier HSV's with the slotted rotors, they had the same rotor on both sides of the car, on one the slots faced forwards and on the other they faced backwards. This certainly backs up the 'stock level' theory. My 2c, Hope it helps.
