That's ballsy on factory tires--even speed-rated ones.
I remember reading that the Veyron high speed runs were made on tires that would last about 15 minutes at full speed due to heat. However, I guess at full speed you run out of fuel in 11 minutes. Making some assumptions on fuel tank size, I'd say at 300 mph you get around 2.5-3 mpg.
That's pretty much exactly what James May said when he ran the Veyron to top speed on VWs test track.
