The new engines aren't that much better YET.
Why?
Because the Alloytec is expected to go the distance, they can only improve it for future models. I'm sure they could push much harder than they have done for the Series 1 VZ but they want room for improvement in the future. They pushed the LS1 from 220kw or so up to 285kw in the later HSV models, and that's not including the GTO or the aftermarket mods people did to the LS1. The Alloytec is a much newer and better constructed engine than the LS1, I'm sure they can do plenty to it, although with all the newer technology I don't doubt it'll come with a price...
Oh, and my S1 VN w/ exhaust + pod was quicker than a riced up 2003 V6 Magna... Surprise!