Depends on the conditions. It is 6 hours by car, but with a BMW or Mercedes you can easily make that 5 hours (averaging just 117km/h). Meanwhile it is 4,5 hours by train, but will likely be over 5 hours due to delays.

In France, Paris to Lyon is 2 hours by train and there is simply no way going by car is faster (legally).

These are just examples, my point is that a high-speed line should be a lot faster than going by car. Not slightly faster, and sometimes even slower.