Even without a supercharger there is still more to be had in the 5.4's
Eg
http://www.aussiecar.com/powerupgrades.html
170rwkw standard to 232rwkw, not bad.
Mind you, this power upgrade costs $4200 incl installation & tune.
btw, the 1/4 mile time of 12.71 was on slicks and a 4:00 something lsd diff. Keep that in mind