Actually the generator that we use is CodeSmith and NetTiers. It is quite extensible and powerful. We have seen no issues with performance, and it is enterprise worthy. It does a great job of getting us through the ORM part of development. We focus on DB, BL, and UI design, getting the data in and out of the database is quick for us (as it should be since it is plumbing).

If you want, NetTiers also has the ability to create business rules to be applied to the entities and build workflows.