I have wanted to see this happen for many years. I am a little surprised they are "only" 4/10s of a second faster than the Cup cars. I suspect the speeds will increase with a little more track time. Having to raise the cars to prevent bottoming out slowed them down some.
Back when Bristol first opened, there were Sportsman & Modified races every Saturday night. The modifieds at that time were well over a second a lap quicker, but they had virtually no restrictions on engines.
There were also Super Modifieds which were more like today's cars. They had open wheels, no hoods and unrestricted engines. I don't remember their lap times, but I know they were quite quicker than the regular modifieds with full bodies.
If you ever go to one Bristol race, this is the one I suggest.