As measured on a shutter speed timer, I have found modern Copals to be quite accurate from 1/2 sec to 1/60....less than 10% off. (just as a reference, 1/2 stop over is 41% over, 1/3 stop over is 26%, 1/4 stop over is 19%, 1/5 stop over is 15%, and 1/6 stop over is 12% over)

As far as f-numbers, using a projection densitometer, I have found the click stops on my enlarger lenses to be right on the money. I don't know the whole range, but from one to the next, I'm always amazed how good they are, better than shutter speeds. Now, field lenses don't have clicks, but these could be measured with a light meter or densitometer. I'll bet they are about as close as you can set them as long as you always stop down from the same direction to remove the play.