Apparently, this ~is~ was a Gentlemen's agreement of the German automakers, to stop the competition for top-speed at 250km/h. Most adhered to it, except Porsche. But nowadays most offer you a special package which will remove the artificial limit, often for another 4-5 digit amount.

I think most production cars cannot sustain that - to say nothing of their tyres. I guess most top out somewhere around 200-225 kph (124-140 mph). And tyres even sooner - 160-180 kph is my guess.