Top Speed stock 5.7?

If your car got "floaty" at 140 something is amiss. I drag race a stock body 65 dart, only change is no front bumper and I can and do go through the traps at 150 to 155 mph on every pass without any sensation of ill handling. Bracket racing can call for some hard braking, and I have stood on em pretty hard from time to time without problems. Most guys start putting spoilers on the back at about 155 to 160, so there is a speed point to be concerned about depending on body style. I suspect the 65 Dart body is more friendly to the driver than some body styles. It is a brick, but may not generate the lift that some might due to the shape of the trunk area.