I have had them on the front of my R33 GTS-t with DBA4000 Slotted rotors for about 8mths now and they don't squeel at all, never once. I've punished them a fair bit too in the last week whilst sorting out some other brake issues and i've found that the harder you hit them the harder they bite back. I did have Greg at RaceBrakes bed them in for me too (well worth the extra $50 odd, I gained alot more than $50 just in braking technique and other bits n pieces he noticed with my car).
First brake he's like "Yup you got air in the rear lines", about the 3rd brake he says "Your front ride height is too low, your car is kangarooing and losing braking distance/effect". The list goes on.... I have certainly never had that level of service anywhere before.
I'll be back there next week getting some more work done