You can, though, get a bit pernickety about this number. About whether impartial verification by, say, the excellent people at Racelogic is enough for you (as it probably is for me), or whether you need an 'official' Guinness world record to make it count. Unlike a 0-60mph run or a Nurburging lap time, it seems to matter. I won't go too far into this but I can see the arguments either way.
I can imagine that, say, Bugatti might want - need, even - the official Guinness title, when it goes after it, and it will, with the Chiron. But that Koenigsegg or Hennessey - whose Venom GT once hit 270.49mph, in one direction only, on the Kennedy Space Center's 2.85-mile runway - might not be able to stand the hassle.
I don't want to big myself up here, but I am the current holder of an official Guinness production car speed record. Yes, really. Set in a Vauxhall Astra. Diesel. In Bedfordshire. But anyway, in terms of expertise it practically makes me a land-based Chuck Yeager.
So, look. If you can buy one, and they've built a few, and they go to the trouble of doing the record, then it counts, for me. I suspect, though, that Bugatti will jump through the requisite hoops. It'll have to. Hard though it is to feel any twinge of sympathy for a Volkswagen Group company, the Chiron is, after all, a 'proper' production car.
I know, the Agera and Venom GT are production cars too, insomuch as that, if you had the cash, you could buy one. It's just that the Bugatti has been built to meet the most exacting standards of one of the world's biggest car manufacturers, even when it comes to, say, keeping the cabin consistently cool when it's 30ºC outside and you're doing 186mph, or how quickly it clears its windscreen of fog in cold weather. There will be 500 of them, not a dozen. It's homologated to all global full production standards. It has been crashed, thrashed and tested in a way that, to put it bluntly, most limited-run supercars are not.
It'll happen, though, I'm sure. Wolfgang Durheimer, Bugatti's current President, former R&D head of Porsche and, I suspect, destined for the biggest jobs within VW Group (because he's brilliant, although it presumably helps that he's also untainted by any emissions shenanigans ), told me at the Chiron's launch that he thinks that a production car will one day do 500km/h (310mph, ish). I don't think he'd say that unless he knows it will, and that he knows it will during the Chiron's production life.
I love that the Koenigsegg Agera RS has already got this close. I love that they've had the balls to do it and I love that they've done it on a public highway. I'm thrilled, too, that they found a public body prepared to close the road to let them. Seems unlikely that they'd let you have a go along the A414 between St Albans and Hemel Hempstead, doesn't it?
But, somehow, there's a car, and a number, that I'm still waiting to see.