Ed,
There is an airfield in Texas (near Austin?) where they regularly do top speed runs on asphalt. Much safer and more predictable than the salt flats I think. Maybe a nice waypoint on your trip this summer
.
Many many cars hit an invisible wall about 150mph where horsepower cannot overcome aerodynamic drag. If you need 250hp to go 150mph, you may need 500hp to go 200mph, and 1000hp to go 250mph. Imagine how much hp is required to push a SR 71 Blackbird to 2500mph
.