They can be Rob, i had Drilled/slotteds on the front and ran them with metal king pads, and greenstuff.
Which your not sposed to
and i did a calder race day, with the metal kings and i was lucky i didnt have any probs with them.
But i have seen them crack
The new DBA Kangaroo Paw discs are alot better at disipating heat, or you could just get big brakes.