Nothing's been absolutely proven yet about track longevity of these rotors. I'll know when they crack.
I would imagine that the main reason these may heat stress sooner is that the rotor wall thickness is less. IE, with the same thickness of rotor, the venting is larger, resulting in thinner walls.
I'm looking into alternate sources for replacement rotors. If I can get the price down to $150 apiece, it might be OK to last only 5 track days.