I see the new GMPP LSX iron block can handle 2500 horsepower.

How much power can a stock aluminum LS1/LS2 block handle?

How much can the stock cast iron block handle?

How much power can an L98 and LT1 block handle?

I would think the GM would have a max power rating for these blocks documented somewhere.  

The LS1 block has been able to handle 1000rwhp and beyond. The real problem is the internals. The stock internals can support 600rwhp and more, but that all relies upon a spot on tune. Unless you desire to go with a longer stroke, the stock crank will hold all the power you can throw at it. The pistons, rods, and rod bolts should all be swapped for someone looking to exceed 700rwhp and do this reliably.  

I was wondering the same thing.  How much rwhp would a stock ls1 with a procharger, p1sc and d1sc, have?  I'm thinking of going with a procharger to get me to the 500rwhp mark and then as cash comes take it back apart and beefing it up so I can turn up the boost.