Speeditaly, bench racing is fun but you need to use better comparisons. The Bugatti (which costs a million dollars+) may have run 434 km, but that is only 269 mph and barely half way to 500 mph. There are lots of $50,000 to $75,000 race cars that will run at least that fast. Building the horsepower to get to 500 will be simple, assuming you have enough money to call Kenny Dutweiler or Reher-Morrison. Then all you need is a good chassis, a crew who can handle every detail under terrible conditions, an experienced driver, lots of dyno time, wind tunnel time, testing, and a perfect course. How much simpler can it get?
You can be assured that all of the cars that run 350 to 400+ mph have done the calculations to see how much horsepower is needed for a certain speed, but even if they had the power, the course, tires, and conditions require lots of planets and stars to align perfectly.