[Assassin]

You don't don't say what driving mode you are in. In Sport or Sport+ it should be nice and tight at almost any speed. Comfort or Eco are much softer. No way should it be floaty at those speeds. Worth considering the road you are on when feeling that sensation. Many highways are heavily worn by trucks etc and in / just after heavy rain you will notice two lines of surface water where the wheels run and little water in the middle or at either side of the lane. Its not noticeable when the road is dry. These depressions are typically wider than a car and can cause a wandering sensation as the car tries to settle into the depression at one side or the other and the driver corrects it without really noticing. It often referred to as tramlining (as it used to be when a wheel got caught in the tramtracks in the city). Make sure your test run is on good quality, flat road surfaces. Some tyres are much more prone to this than others.

If its floaty in all modes it needs checked out in case of alignment or suspension issue.