The 4.0 Mustang motor is probably more similar than you think... their dyno graphs are about identical until about 4,000 RPM where I believe you start seeing the VVT really shining on the LLT... at that point the LLT graph takes off...
Also.. you mentioned the perforated x-pipe... found the diagram for that:
I have the feeling that this x-pipe is really absorbing a lot of sound along with the two mufflers... giving the system it's refined but quieter sound...