got boost?
they do stress the engine more, but it really depends on how you drive it. I dont really know if the added stress would manifest itself over the life of the car, especially if the system is modest boost(~6psi) and tuned properly. The nice thing about centrifugal SC's is that they arent really going all the time, and although this means most of the kick is high up, it also doesnt stress the engine as much down low, where you drive most of the time.
You know though, there are some nice cam kits available too, although the ESS kit may allow you to outdo the E46 M3.