Tom at Scat has told me on more than one occasion that the sb mopar cast crank they sell will handle 600HP. This does mean with no detonation.

I believe it, however...I won't use the cast crank in a trans brake application, and I recommend if your going to build more than 500HP AND use a 4 speed not to use the cast crank.
NOS is another no-go for the cast crank IMO...it really depends on the application, intended use and how well the owner takes care of it/drives it.

If it's a driver that might see the track once or twice a year with a 4 speed or small NOS kit and it's used properly it'll last a long time.

Be HONEST with yourself about how you will use the engine and then make the choice that makes sense.
Easy!!
Brian