[SpdBoss]

looks like most of the gain is with torque on the bottom end. by 5750rpms the 4.6 is doing better stock for stock.

main issues is exhaust, and intake. they sell an intake for 625 to go onto the 5.4 and everything fits under the stock hood. oil pans swap, front accessories swap, all sensors swap. stock headers will fit but the h pipe has to be extended on both sides to accomadate for the wider taller deck height.

as you already said, cams for the 5.4 are the same for the 4.6 so maybe with a cam swap it could be worth it.

here is the chart