I still don't buy the whole 150 mph thing in a stock hemi. Lightning's and SRT-10's barely do 150, and they make a whole lot more power then a hemi. You say top speed is all about gearing, but aerodynamics(sp?) plays just as big of a factor.
I remember reading an article from Road and Track I where they test a few supercars in a 0-200 test. The owner of a 205 mph Lamborghini changed the wheels and slowed the top end down to 190.1mph.
Road & Track Magazine - Lamborghini Murci�lago (9/2007)
so just by changing to a less aerodynamic wheels, the car lost 15mph.