It isn't once you start getting over 200, it is when you have a poor coefficient of drag and keep trying to push it higher and higher. Since the McLaren F1 has a better design it can go further with less power. That is why mathematically with the same power it would hit a far higher top speed. That is why the Veyron is overrated, it needs a ton of power to push a comparatively poor design past something done in the early 90's with far less power. Goes to show you which was engineered better.
As the drag increases as a square of the speed, the power requirement increases as a cube of the speed because the power itself is speed-dependent. The Veyron because of its high CDA figure and huge cooling drag needs 1001 hp to go 12 mph faster than a McLaren F1 producing 627 hp. To help understand the problem of starting a car program from a weak point aerodynamically, we do some calculations: A turbocharged F1 producing 1001 hp would achieve 281 mph assuming the same drivetrain efficiency. Another way of looking at this equation is that an F1 would need "only" 740 hp to reach the Bugatti's top speed. All this demonstrates just what an uphill struggle the Bugatti team faced to achieve their targets.