Ian, the potential problems associated with drilling you describe are pretty well understood and should be avoided by using the correct tools and machining parameters. On my appreticeship if I was ever caught in charge of any machine that was chattering or with signs of blueing on the cut surface i'd up for a severe dressing down in front of the lads'. It was a serious no, no! The reason is that when you were unleashed onto the shop floor and put in charge of a machine that was cutting metal on a component that was worth more than 10yrs worth of an apprentice's wage you had to do things right first time.
I suspect cast holes are a by-product of making the manufacturing process cheaper rather than solid engineering performance reasons. For example the disc will be heat trated to harden the surface, which means you cannot drill the holes before heat treating the brake disc surface due to the possible distortion and warping effect on the disc due to the drilled holes, and to drill the holes after heat treating the disc surface would massively increase the cost of your tooling due to the harder surface of the disc eating drills for breakfast. Therefore by casting in the holes and only carrying out a light finishing cut on them after heat treatment would massively save on the cost of drills. Just my theory anyway.
Seems to me that the discs with cast in holes are still not resistant to cracking. Porsche 'drilled' discs, that supposedly have cast holes, seem just as prone to cracking as any other 'drilled' disc from what I read. This is why alot of the GT3 chaps are reverting back to solid discs as the drilled ones are only lasting for a handful of track sessions in some cases. I guess they must really be driving them hard though.
Anyway back on topic - drilled discs are perfectly fine but for hard track work you should be aware of the possible cracking issues.
Scotty - with regards to EBC yellows. I've got them at the moment. They are far better than EBC reds I had before which I found to be simply dangerous when cold. So far i've found the EBC yellows to be much better, they have good cold bite and i've not noticed any drop off in performance when temps get high on track. However I am disappointed with their feel - i.e. you don't get a progressive increase in bite as you push harder on the brake pedal, so they feel a bit numb, but in terms of out and out braking performance they are perfectly adequate. They can squeal at low speeds, but not all the time and certainly not embarrassingly so. I would love to go with Performance Friction pads next time, which by all accounts are supposed to be unbelievable, but since the car is my daily runner I couldn't live with the copious amounts of corrosive brake dust they seem to produce. I might even go down the route of swapping the pads for trackdays like Paul, so I can use PF pads for trackdays and stock pads for street as i'm planning on a second set of trackday wheels so it's not a big job to fit different pads while i'm in there. I've not really had enough experience with other pads to particularly recommend them over any other brand, but I would not recommend the reds. If you go for EBC's then go with the yellows.
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