What was done to your head as far as 'work'? Was it flow benched after? What cam profile was it ported for? Were the velocity ramps ground out of your MKIV intake ports? What you had done to your head is going to play a MAJOR role in your torque curve. Then there is how the SRI was designed and what rpm the harmonic wave was designed to hit at. Then there is header design that effects your low and high end torque peaks. Lots of head variables here...all parts of the puzzle.
Stock 8v heads stop making torque after 4500rpms. Better flow just keeps it from dying as fast. Getting all the bolt-ons and headwork to work with each other is the key here.
This is my before/after dyno from 2008. Even with a 288*, my peak was between 6000-6500rpms. Still pulled past 7000rpms, but never shifted past 7200. Its at this point where you need to run a REALLY large cam to move the peak powerband up into the 7000+ range. And that's not daily-drivable. Or inexpensive!