It's functionally impossible to drive at 250 mph for any meaningful period of time. Drag is a gigantic problem (as james may says "it's like driving through custard"), not to mention the fuel requirements to go that speed. One of the bigger problems is actually tires. The veyron's tires can only last ~20 minutes at those speeds and a new set is 20 grand. If you want to go those speeds you can't do it in the open air (unless you're actually flying) and you certainly can't do it on rubber tires.