last width is the least important factor when shopping for a ski boot. the number that the manufacture puts on the box is a target for fit and marketing of the product.
unfortunately for boot fitters and skiers there is not a standardized system that exists to solve your line of questioning. actually it is only unfortunate for you chemist, and for really good boot fitters it is the reason why we continue to flourish in our business.
so the dirty secret is that you possess the magic to unlock what we all know. your foot!
your foot placed in any boot on the market is the magic bullet which will determine last width, length, instep height and volume.
to have the best chance of making this happen it is very helpful to find a spirit guide ( an accomplished boot fitter, that has many brands and models to chose from, that has had the ability to try on and ski on each model that they have in their store)
what are the pitfalls?
on this forum, most of the boot fitters work in shops that only stock so many brands, and so many models, having to make choices as to which ones will sell the best. because of this you will get recommendations that are limited by that conundrum.
secondly if your boot fitters are not involved in some form of product testing, the feedback from boot fitters will be limited because they have not skied on every model from every brand that they are recommending to you. how the boot fits while skiing is a stronger form of knowledge than how the boot feels in dry test at the shop. ( also should have a light bulb go off for you that good fitting performance boots like you had, will need to be occasionally adjusted to keep the fit good and the performance up)
now this is the tricky part. you are the difference between having success in your boot choice, and the communication with your boot fitter to make sure that your goals are accomplished. to make it happen you need to immediately walk away from your computer and find that skilled spirit guide that i mentioned above.
if at this point you are still reading and or searching the site "crapthaticangetforcheapskideals.com".....forget about it! flip a coin, order on line, and then get frustrated because all of the wonderful advice you gleaned from the boot guys and all the helpful bears with feet, legs, goals, and skiing style that look nothing like yours chime in on the best boots for you.