My buddy's '03 Z06 is currently putting down 664rwhp and 564rwhp on bonestock longblock LS6, however this is with turbos. The reason I bring this up is, the torque of the turbo comes on so progressive and late in the rpms that you can get away with more over all hp compared to a nitrous set-up. Though a nitrous car can be set to mimick a turbo curve, as shown below. Really it is the low rpm torque that does the damage more often on stock blocks, not the HP. I finally busted a ringland on stockblock LS6 with 665rwtq @ about 3200rpm. So multi stage (my choice) or progressive can allow a higher overall HP by limiting the low rpm torque.
Here's my buddy's turbo set-up, check out how slow the tq comes on, and how late the torque peak comes, compared to some of us that have the mega tq spike down low.
and here's the turbo/nitrous overlay showing n2o can be set-up like a turbo (these are small hits just for reference, but you get the idea). Mine was dual staged, while Joe's was not.
Robert