I'll have to go the other way. I needed a battery quick once for my '51 club coupe. The only battery available on short notice was a group 1 with 425 CCA. From the time I installed it, I had a hard time starting the car when it was warm. Cleaned grounds and replaced a few components to no avail. Finally put in a proper sixed 725 CCA battery and have never had a problem since. There was a reason Ford engineers designed these cars with group 2 and 2L batteries instead of group 1.
I don't doubt that a smaller battery might work in a race car where everything is out in the open, but when your car is sitting on hot asphalt on a 95 degree day and you run into the store for something, you might appreciate the extra CCA's when you come out. It got to the point that I would always open the hood when I parked the '51; people thought I was wowing them with my stock engine. It actually was the only way I was sure it would start.