The 5.4 probably can't rev as hard cause of the longer stroke, so the power potential is prolly lower with teh 5.4. There are a lot of new forged internals for that engine and they're not priced cheap.
Is anyone else worried about the displacement defficiency in the new modular engines? With the Windsor, they had a rediculously oversquare engine (302 was probably 4x3in). And Ford had bigger displacement engines in their lineup like the 428. These days, the modular engines come in 4.6 and rediculously undersquare 5.4 and 6.8. I'd assume to build bigger modular engines, bigger "modules" would have to be engineered and that would take some time and effort.
True our 5.4s have 32v and dual VCT, but even technology has it's limits. Look at a BMW M5, 5.0 32v with VCT - 294 kW. The GT Barra gets an extra 0.4l in displacement but probably won't make the 7000rpm redline, so it's maybe not going to make a lot above 300kW NA. I reckon the Barra 5.4's got a bit more to go, seeing as the dual VCT phasing hasn't been individually mapped yet, but if Holden's gonna be looking at doing silly things like strokers and the Gen4, Ford should probably be looking at getting something bigger that revs harder. That said, anyone who looked down at the 40yr old pushrod iron dinosaur Windsor that still matched it with the latest and greatest Gen3 and turbo DOHC cars should be absolutely blown away that an engine of this caliber is available in a car under 60k.