My uncle, Chris Werner, bought kenny duttweiler's red regal in the late 80's. Kenny turned it into a super stock c/x car with an n/a v6, for Chris, and Chris later sold it to billy chaffin who turned it into a cop car.
It was a test bed for buick's stage parts and ran 10 oh's...it was a pretty heavy car as well.
Anyway, he kept snapping steel nascar cranks. One after another. After some extra oil mods, ultra balancing and race prepping a cast crank, they never lost another one. It lasted forever. What kind of rpm's does this motor see?
600hp out of something like 262 cubes, and goes through the traps at 9600rpm!
The bad thing about steel cranks, is that it has "memory". Once it sees enough detonation to distort it or sees an abnormal amount of load that twists it into some weird shape, you can throw it back in the crank grinder and grind the distortion out of it, but once running again, its going to want to form right back into its distorted shape because the crank has lost its tensile strength. It twisted beyond the yield zone. Once that happens, things break again.
Cast cranks dont do this. If you have something happening, thats violent enough to snap a cast crank, then the problem isnt the crank. Steel is a band aid for another issue.