You can turn it as hard as a steel for awhile, then it is subject to failure. Some people run them because they are lighter than steel but they don't last long under extreme circumstances. I know of several cast crank 521 inch Ford motors. They turn the rod journals down to stroke the 460 BBF motor and they last forever it seems. The ticket is they don't run high RPMs with them. Hope that helps you a little. RM
My old cast crank 406 saw 9000 on a few occasions, and 8000 numerous times--I never ran a rev limiter until recently, and with an 8000 rpm chip the car kept slowing down because it was hitting the limiter.