sonic checking blocks

If you are building 450 plus hp motor its a good ideal to start out sonic checking the block before dumping a lot of machine work money in it.
However the real question is what is to thin to build I have a .040 over 340 that has a minimum .145 wall thickness and I have heard this is a little close however I have run it stroked at 500 hp with no block problems.

I'd be interested in other members sonic results of factor and race small blocks.