I hope we didn't wig you out too much. Frankly, I don't have any data that suggests that Boxster motors crater at any greater rate than others.
The RMS issue is real though and no, we don't have any reliable publised numbers on how likely you would be to get one.
If you develop a good relationship with your service advisor at Porsche, he will give you tons of good infor on the car, most of which is never published.