I have had the Stillen set up (with non drilled slotted discs) for nearly 5k miles now. It is great, but allow me a couple of comments...
1) Any fading of the stock braking set up that you might experience on the road is due to the brake fluid boiling. Swap the stock fluid for Castrol SRF and it should solve all your problems.
2) if swapping the fluid is not effective and you cure the spongy pedal but you are still getting some fading then upgrade the pads to racing pads (pagid RS29 work great). You will have to put up with brake dust (I painted my wheels black, so no problem there) and some squealing.
3) the main benefit of the stillen brake set up is that it has larger, 2 piece, full floating rotors. This will allow the heat to spread over a larger surface, increasing the time it will take to get to the fading point (using the same components).
4) even on the track I have never experienced fading with the stock system. My pads and rotors would last 1 track day (the pads in the front would actually last half a day), but it was the tyres overheating or finishing the fuel that would force me to stop, not the brake fading.
5) The Stillen set up is standing up to the track abuse fantastically. I have done 3 track days and a 2k mile trip across Europe (with braking from 200mph on the Autobahn) and had to change the pads once. The rotors are still in great condition.
6) I suppose the 6-piston caliper acheives a marginally higher clamping force than the stock one, but again the limit is the tyre, not the caliper.
6) The AP Racing calipers look great, like Ed said. The car should have come with 6-piston calipers at the front from the beginning.
All in all I am super happy with the set up. It does exactly what I hoped it would. It is pricey (I bought it early and had to pay some 18% import taxes for the UK on top) but in the long it is saving me money, as I d not have to keep replacing rotors and pads.
Looking forward to Ed's and Stormcat's reviews!