They added the restrictor plates since 1988 for Daytona and Talladega super speedways. During high-speed spins the cars were getting airborne and only luck kept them from punching through the fencing and going into the grandstands. The flaps that flip up when they spin were added for the same reasons. I think 204 mph was the Daytona record for qualifying before the restrictor plates were added. They sometimes get airborne in the current confguration.
204mph sounds about right for the Daytona lap record. And Talladega was even faster; Bill Elliott pulled a 212.7mph lap in qualifying for one of the 1987 races there.
Given the extra twenty-plus years of engine and aero development on Cup cars, I wouldn’t be surprised to see one turn 220mph laps at ‘Dega with an unrestricted engine. Which is probably why it wouldn’t be a good idea; I suspect the day one of those cars clears a catch fence and lands in a grandstand will be the day motorsports dies in this country.