Actually the ref 36 and 54 both have lower arch necks. The series III has a mid height arch, but the end of the neck turns up more towards the end on the III and as a result it's not as comfy as the Ref necks. I have a Ref 36 and 54 and a series III neck. The Barone is a hair lower in arch then the III neck. The ponzol is a very high arch neck.
The truth is the series III arch is higher than VI. The refs on a whole are a hair lower arch than most VI's, but the Ref offers the closet match for the VI and not what Selmer has printed about the III being close. Now some of the later VI's might come close to the III, I don't know.
Here are some pictures of my III and ref 36 neck. The 36 is on the right and the III is on the left it has red dental floss wrapped around the cork. You can see from these pictures that the neck with the detal floss is higher.
http://img.villagephotos.com/p/2003-11/513693/GKPLF-100_0547.JPG
http://img.villagephotos.com/p/2003-11/513693/LDPZY-100_0546.JPG
Here's a picture of the Ref 36 and Ref 54 necks side by side. You can't tell a difference in angles.
http://img.villagephotos.com/p/2003-11/513693/SLZML-100_0556.JPG
http://img.villagephotos.com/p/2003-11/513693/HNLEH-100_0555.JPG
My Ref 36 and 54 side by side.
http://img.villagephotos.com/p/2003-11/513693/JEWXY-100_0517.JPG