According to a 1966 Autocar road test of a 2000 auto, in top gear it gives 19,5 mph per 1000 rpm, so 4000 rpm corresponds to 78 mph and 5000 rpm to 97,5 mph.
On the test car the speedo was showing 3 mph more than the actual speed.
On normally brisk acceleration from rest (whatever this means for an SC auto) it changed into the 2nd gear at about 25 mph and into the top gear at 55 mph.
With the accelerator to the floor these change points were raised to 38 and 68 mph respectively. (It seems that the testers were brave enough, after all it wasn't their own car...
)
They do mention the two yellow dots in the speedo at the 47 and 78 mph as the maximum permissible speeds in low and intermediate gear.
I suppose that they correspond to the red line in the tacho, which begins at 6000 rpm in a 4 cyl.
Top speed was 94 mph.
So, there you go, you know how a new car was. Obviously these figures will have to be adjusted for a worn out or tired car.