I really think the bottom line of how much it can handle is really in the prep of the block and parts and how it's set up. Not having the rotating assembly balanced good enough will cause stress, high compression adds stress, etc. Then there's un-known's and things beyond our control such as weak spots in the castings of the block or rods. I think there are a lot of variables involved. There are going to be those who have pushed 800 HP out of a well built and regularly refreshed build, and then there will be those who break at 450HP.
For many of us, if we had a stock block engine grenade with 500HP, then we'd probably not try to push it that far again, and be under the impression that a stock block couldn't handle it (unless we found the source of failure to be something else).
I just think there are too many variables, and there's going to be all kinds of opinions, probably based on way more experience than I have, that will range from one end of the spectrum to the other.
