While it may only be a bit over half the Earth's gravitational force when averaged, it would reduce significantly as the car approaches top speed. And also, the car can get to 410km/h and not go faster purely because someone realised that was probably about fast enough, and not because it is physically incapable of higher speeds. I'd say that's pretty damn impressive.
Right, we'd need access to the position vs time graph so we could take the 3rd derivative to find the change in acceleration over time. Then we could talk about the maximum instantaneous g force.
You gotta ask yourself though, do you really need to go that fast? Most average people, unless they rob a bank or are stupidly dedicated to never being late for work, really have no use for ever going much over 80 mph.
Can't speak for them, I think they are insane but my car also can't really go over 70 mph and would probably shake itself apart or explode if I pushed it to its max 90.
*cough*AUTOBAHN*cough*
I fucking shit you not:
http://koenigsegg.com/regera/