Well a heads/cam LS3 can hit well over 500 whp easily... If you want all out n/a power you can't beat an LS3. I would probably go with a 5.0 given the choice, but I would hate to hit the wall after bolt ons your only option is nitrous or $10k f/i build.
Most 5th gen owners don't mod their cars how they should though, they ignore things like rotational mass and weight and gearing. Like the one the op raced in the first post.
Not sure why you think a 5.0 hits a wall after bolt-ons. You might should stick to the Camaro5 forum. The fastest all motor gen5 Camaro I've ever seen at SGMP was the Jbrown guy on Camaro5 and I raced him on his best ever pass which was an 11.36@121. I can list all of his mods if needed including cam specs and the only thing stock about that car is the rotating assembly.