Talked to a 944S friend last night. FWIW, they are running a wider tire on the same sized rim in a 100lb lighter car.
He says the early tires had a HUGE problem with splitting (75%) it seemed to be limited to their size and just the early tires. The newer tires are better.
He and the others that are competitive with him are also finding that the tires are good for no more than 3 weekends, but he thinks they are fast all the way up to 15+ heat cycles. He suspects proper scrub in (i.e. let them rest for 24 hours or more) might be the key.