These speed charts are only theoretical speeds, they won't take into account wind, tire resistance, etc. which is usually what tops out a car. Cars usually run out of HP before they run out of RPM.
This is what is limiting the speed of my Crossfire to 154mph. It runs out of HP before the PRM hits redline.
Granted your 408 will have more HP than my Crossfire but you are trying to push a brick through the air while I am pushing a car with a lower drag coefficient.
Chuck
