You need more information. Are you planning on using just one boat ramp (OK 90% of the time). Hang out at the boat rmp and take a look at what vehicles are handling the job well and what vehicles are having trouble.
Go into the marina and ask the people operating the ramp what problems they see and what cars they would like you to use to launch a boat at their ramp.
In short you will get better answers from people that are more closely involved with doing what you want to do.
So the Mustang is a wheel spinner,ask yourself what specification puts the Mustang in wheel spinner class and avoid this quality in your perspective boat launching vehicles.