In the 60's I would drive my stock Model A at 50 to 55 with the modern traffic at the time going 60 to 65. Today a stock Model A is best kept to the side roads unless on an LA freeway where the traffic flows at 15 mph.
With my Model A today, with Burtz block, HC head, cam, overdrive, and downdraft Weber carburetor I will drive 65 on the highway with the modern traffic going 70 to 80. I love the back roads where I can cruise along at 55 or less and run through the little North Carolina towns. One of the nice things about North Carolina, that I love, is the little towns and the winding back roads.