I agree. I think that simply the fact that the CONVERTIBLE Veyron can still do 253 should be proof enough that the normal car can do much more than it's claimed top speed.
Bugatti is king. The Veyron is currently the best car in the world (I'm saying best, not my favorite) because it can do what it does with an ease that simply no car can match. Here's some info to prove my point:
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-The power output is actually more than 1000, but 1001 has "a nice ring to it".
-As you mentioned, Diablo, it is limited to 253. They mentioned this on Top Gear, as well.
-The Veyron Pur Sang, Pur-somethingorother, convertible, and Hermes Editions can all do 253, so I think the genuine top speed is more.
-The Veyron is EXTREMELY stable at high speeds, something even the Koenigsegg couldn't manage.
-The audio system alone is worth $30,000.
-Each stalk on the dash is worth around $1,700.
There's more, too...
-Leadfoot