I recently had a discussion with a senior acceptance pilot from a mainline carrier and he told me that one of the acceptance tests was disabling both packs at cruise alt (max differential pressure). The resulting cabin ROC should not exceed 2000 fpm. I will try to substantiate it with a doc.
--from Boeing 737NG production flight test procedures:
So apparently this is for new aircraft from the factory and its not a regulation source. But just FYI.