The S197 GT is governed at 145 mph. Although the speedo will likely read at least 5 mph higher. If the speed limiter is disabled they top out around 157 mph.

Cars with more power have an advantage in top speed.
Its almost all about horspower vs frontal area / cd.
Power to Weight has very little effect.
A stock Charger R/T is likely faster than a Mustang GT with disabled limiters.
Most Land Speed Record care are actually weighted to increase traction on the salt.