Cast crank rpm?

My guess would be something other than the crank will give you problems first. Not a SB, but I fooled with an old bracket motor (440), a friend bought. Ran 10 years with a ton of boost from a 6-71 supercharger. Ran another 3-4 with different heads, (10.6/1) in a bracket car, spinning 6,800 rpms. We detuned slightly, and it's still going strong. I bounced it off 7K a bunch. Cast crank.