Dumb move, but I did it:
135 MPH. Car: 1995 5.0 Mustang GT. When: January, 2000.
Where: I-95, south of Philadelphia  VS. Porsche 944 Turbo.
Things happen NOW at that speed. Slower traffic caused the ABS to activate and the car shuddered and did not feel like it would stop in time.
Foolish behavior acknowledged.
Please note posters: Most cars 10 years or older have incredibly innaccurate speedometers above 80 MPH. They all start to register high, as much as 10 MPH, and sometimes more. 
Many posters are out to demonstrate how fast some older muscle cars are, but they just couldn’t generate speeds higher than 120-125 MPH, and that’s on a long course. When equipped with an automatic, the car wouldn’t usually top out in the highest gear, there’d be slippage in the tranny, and the awkward body shape couldn’t get through the air. 120-125 would be the ceiling for many 60’s and early 70’s muslce cars. Sorry, that’s the truth.
Thanks to the Grand National owner for his honesty. The GN doesn’t have the body shape to be stable above 125. I’d kill for a GN, because there are more chances to enjoy awesome acceleration than top speed runs. 