Apart from what the title of the thread says, i.e. in practical terms stop down halfway down the scale (where you usually find f/16-f/22 for 4x5" lenses), the question seeem to be about DoF. If you do a search for e.g. "large format" and "DoF scale", I recon you will find lots of information on the subject (apart from Ken Rockwell's excellent article). I do personally use this DoF tech. all the time when I shoot LF and have done so since the 80'ies. It's built into every Sinar camera since the F and P series were introduced and really makes life under the dark cloth much easier. All you have to be aware of is that these scales often are designed with a final print of 8x10" in mind. (The DoF scales of most 35mm and MF lenses also have the same target, i.e. a 8x10" print.) If you want to print bigger, you have to stop down more and then it's good to know the formula with the acceptable Circle of Confusion etc. (Which should be in the Ken Rockwell article as well as on other places.)
Oh yes, about the 1/3 - 2/3 vs. ½-½ thingy. When you have set the focus, it should be halfway between the far focus plane and the close focus plane. That is what happens on the film plane side of the lens. On the other side of the lens (i.e. the real world which isn't upside down ) the close focus plane is at about e.g. 1 meter (OK then, 1 yard for you americans), the actual focus plane is at 2 yards and the far focus plane is at about 4 yards. So it's both 50-50 and 33-67, depending on which side of the lens you are.

What I don't understand in some of the above answers is why you talk about different lens designs. Every lens of a specific focal length does have the same DoF at any given aperture opening. This regardless of it being a simple meniscus lens or a complicated zoom lens.

//Björn