I was running 12.4 with 266rwkw on an Eco. You're focusing on the wrong numbers, it's only 6 cylinders. If you pushed 400rwkw out of an alloytec you'd be replacing your engine and drivetrain every other week, that boosted LS would look mighty tasty to your wallet and eat it for lunch with its eyes closed
My current beast makes just under 400rwkw but it cranks out nearly 850nm, you won't get that from an alloytec before it's in pieces on the dyno. I can add plenty more power before it bothers the setup
One of the guys from Outlaw Speed Shop in Sth Aust., has somewhere around 400 - 500 RWKW on his V6 VE engine...
I can't remember his name - but he has done it & from memory its his daily driver....
So 400RWKW is NOT a fantasy - obviously one would need to strengthen their internals before applying such boost to get those numbers
So realistically its all about what you put into the engine....
& yes obviously being a V6 alloytech engine one would start getting up to the top end of the capabilities of that engine
But then again, remember the days when the Barra engine would do 400RWKW & it was getting to the top end of its capabilities
Barra's can now safely do 1000RWKW & still be driven daily - As goes for other 6cylinder engines.
its all about what $$$'s you spend, the research you put into the project & your expectations given the $$$$'s spent