Well, after all that all I can say is that the speed is right around 180-185 mph. It doesn't matter if its aero or gear limited. Not sure how to put this, but the error on the aero drag causes it go from aero limited to gear limited. A bit less drag and its gear limited (in 5th), a bit more and its aero limited at ~6000 rpm.
I can't find a dyno sheet for the 3.5DI. I imagine it probably drops off a bit before reaching its peak.
*edit I just found this, anyone want to fill in the blanks?
speed-calculator