Any significance in strength between stock 360 cranks and the cast aftermarket 360 -

You'll probably find as many opinions on that as the "need a new block" thread...lol.
The end result has to justify the means IMO (cost vs. return). Every part has a life span. Some will never reach the end of it, some will. Generally, the stronger the crank, the lighter, and the less flex due to normal harmonics, and better the surface for the oil wedge to work with. So while any engine IMO can benefit from "the best", not all will ever reach the point of needing "the best". Not that it's a really straight answer, but to me, to get a straight answer, you have to ask a direct question. "When will it break?" is too dependant on a whole series of variables.