I guess it's up to someones opinion, what they want to risk, and what type of rpm's you'll be running.
I was recently reading a "How to Build BB Power", or something like that, and it states a cast crank and 2 bolt block can handle 600 hp. After just recently tearing down a 454 with a cast crank and 2 bolt block, I'd tend to believe that, or more. The journals on the crank are huge, and the main caps are very large to. A two bolt bbc should never be compared to a two bolt sbc, those main caps are puny to say the least.
I'd guess if you added splayed main caps to a 454, and run a forged crank, you could probably through just about anything at it.
You could ask over here,
http://speedtalk.com/forum/index.php
There are some real engine guru's over there,
.