Well...think of it this way: Lets say theres a car taking a turn too fast and its gonna crash into the wall. Would u rather be strapped to the hood of the car or strapped to the trunk?
Id rather be on the trunk. My body will have the same momentum regardless, but this way I would be using the car as the "shock absorber" to cushion my impact.
If you figure out how little the difference is, I think you'd reconsider this. The only difference to your internal organs, and bones in the scenario you describe is how fine the paste that was your body will be.
The crumple zones on a car are designed to absorb about 10 MPH of kinetic energy/foot 1 foot crunched in car, it hit at about 10 MPH.... 2 feet= 20, 3 = 30 etc. The car crumples, because there's about 3,000 lbs of mass involved. When the car comes to a stop, and you hit the trunk...... you don't have the mass to make the car crumple in.
The only differential in speed would be how much the nose of the car crumpling slows down before chassis you hit the back. If you are both doing 60, and the car hits a cliff and stops completely.... you're hitting the trunk at 60. 88 feet per second.
For a general reference on what that sort of speed means--- if you jump out of a second story window, you will hit the ground at 25 MPH. 36 feet per second.
Jump off a 100 foot tall building. You'll hit the ground at about 60 MPH.
As they say, it's not the fall that kills you; it's the sudden stop at the end.
Personal 'crumple zones' are limited to being useful over speeds that nature could expect people to hit -- 10-14 MPH.
Best not to hit anything, going faster than that.