Wasn't aware of the 4.6L choice. As you say, not much of a decision there. The 5.4L is an exceptional engine. You do, however, need to keep your foot in it to get maximum benefit...where I like it most is 3,500 to 5,000 RPM at full throttle. In both first and second gear, you get a very satisfying push by it hitting its HP peak.
Of course, you're swilling the fuel at an alarming rate by doing that too much.
Fortunately, there is amply sufficient low-end torque for your RPMs to rarely crest 2,000 in normal driving.
Also know that the 2004 change to IRS makes the second generation of Expedition very appealing. Goes down the road very well. I call it "driving my couch". My wife agrees.