Try this link and start plugging in information.
I just plugged in the info from my 1 dyno run and it spit out the exacty same HP figure as show on my graph. It said I had a theoretical top speed of 167mph.

http://vlsicad.ucsd.edu/~sharma/Potpourri/perf_est.html
http://vlsicad.ucsd.edu/~sharma/Potpourri/perf_est.html

Also, if you are trying different top speed calculators on the net you may also need the following:
Cd: .37
Frontal area: 20.56 sqft
Drag area(CdA): 7.6069 sqft

Here is the gearing info for the SRT 6 you will need to plug in:


Transmission Gear Type 5 Speed Automatic w/ Overdrive Final Drive 3.07:1 1st Gear Ratio 3.6:1 2nd Gear Ratio 2.19:1 3rd Gear Ratio 1.41:1 4th Gear Ratio 1:1 5th Gear Ratio 0.83:1