I'd also love to see a chart sketching out changes in width and length as one traverses the various sizes (I know the issue of whether there is a uniformly graduated increase in length and width as size increases was discussed, but I can't recall what conclusion was drawn).
According to 'Resistant' and the sources that he has drawn upon:
"A last has a certain determined starting size and every E is 3/16 of width EE is a 3/8ths of an inch difference."
...Sounds convincing enough to me.
(conclusion: the unit of measurement difference between widths is constant along the sizing spectrum. (e.g. 7E is 3/16" wider than 7D. 12EE is 3/16" wider than 12E, ect.))