Does it shake in the steering wheel or "in the seat".

Steering wheel = front setup
"In the seat" ususally rear setup.

The cardan shaft is a direct drive output so the higher the speed of the car, the faster rpm of the shaft. For that type of severe vibration I'd take a look at the shaft, that it's tight, plus also the tranny mount so the shaft doesn't have to act like a CV joint.

If you can do some "slalom" at those speeds (afterall the car has PSM), to load and unload to the left and right, does vibration increase or come and go. Then might be related to halfshafts.

Wheel bearing usually make noise firsst, then "fine" vibrations, no severe vibrations.
CV axles would give a lot of play when you go "on and off" with the pedal, if only one side possible a little sidejerk, alt "oscillating" feeling in the car under medium acceleration.

Best of luck.

 

It shakes throughout the car and through the wheel. Passengers are just as aware of the shaking as the driver.