Plenty of guys making big power on stock internals with no issues. They are a well put together setup overall, just need some more oomph, but they can easily handle it.
LSA has been out for quite some time in the CTS-V. ~650Rwhp is the safe limit on stock non-forged pistons. Of course, you can build over that and roll the dice, just like all the GT500 builds over 800Rwhp.