David,
There have been several blown motors from high RPM track use. Others have run the same way with no issue. The same happens to 944's.
The current thinking is to use an Accusump, shift at 6K max. and check/change the rod bearings ever few years if you do a lot of tracking.
Drilling the crank and using an Accusump seems to be the safest way to track the car at high rpm shifts.
www.928intl.com has a write up on why they drill their crank.