It's like this fellas. In the 60's, engines were measured in gross horse power, meaning total output, including what is used pull the accessory belt(s) and timing chain. The original GTO peaked at about 360 of those. Today, we measure net horsepower, meaning what the engine has left after it powers it's accessories and timing chain. The difference is something like 60-75 hp. Thus the reason 360 hp engines suddenly dropped to 290 hp. It had very little to do with octane, even less to do with lead and a lot to do with a change in the unit of measure. But this does not tell the whole story either. Chevy engines in the 60's were just as inefficient as Pontiac engines and hp:cid ratios were just as low in most cases, the exceptions being the 454 LS-6 and the 427 ZL1, neither of which were ever really suitable for street use.
What is my point? Ponder: the 5.7cd LS1 weighs a lot less than the big blocks, due to aluminum construction. Adjusted for differences in units of measure, the LS1 is actually MORE powerfull than the original, even if you use the understated (for insurance purposes) figure of 320 nhp (about 395 ghp), which is actually more like 370 nhp (about 445 ghp, approching the LS-6 454). Further, the 5.7cd LS1 is due for a retuning of its heads and cam which will bring it's advertised net horse power up to 405 (about 480 ghp eclipseing the LS-6 454) and actuall nhp to about 455 (about 520 ghp, eclipseing the race only ZL1) Further, the current 5.7cd LS6 gets 405 advertised (see above, compare to the original LS-6 454) and is actually closer 455 nhp (again, see above and compare to the ZL1), is due for an upgrade next year that will bring its advertised horsepower to 450 (equaling in nhp the ghp of the original LS-6) and will probably be closer to 520 (ghp will almost reach 600).
I would say to anybody who is complaining about the engine in the new GTO and Chevelle to reevaluate the numbers and reconsider. I for one will refer to walking into the pontiac dealership as "seeing a man about spanking a pony!"