I don't think you have to worry about the quick growth issues if you are crossing standard breeds, even big ones.
The breeding stock used to produce the Cornish cross meat birds has been selectively breed for generations in order to produce the fast growing meat bird offspring. You won't run into the health problems when crossing standard breeds that you have access to.
For instance, if you took a Standard Cornish and crossed it with the biggest Rock you could find, the offspring would not suffer from the health issues associated with very quick growth.
Anyway, in my poking around the web looking for information on meat birds, I have occasionally come across a post from someone who wants to breed their own meat birds by crossing Cornish and Rocks. The replies are always along the lines of: you ain't gonna get anything like a Cornish cross that comes from the hatchery.