I'm not a big physics major, but just from looking at the available stats, my guess is that it probably doesn't do 250-260 miles per hour. The stats for one of the most important variables - the transmission, are pretty sparse. Who knows what the ratios are? I assume it's a six-speed, which would make 250+ kind of unlikely, while still being a streetable road car. Plus the final drive ratio is not too unlike a Diablo VT.
Also the tires, Michelin MXX3. Any tire capable of withstanding those speeds is very specialized - basically developed for that one car. Like those of the
Veyron.
If little Vector could achieve all that with the Avtech, the Veyron is even more inefficient than many think.