On Tuesday, I visited Kevin Leahy's custom bootmaking shop. He makes extraordinarily beautiful custom hiking boots - and to do this, Kevin uses some of the nicest machines I've seen. He generously let me try his sewing machine (I've nearly destroyed my current machine, so I'm researching industrial machines) and spent a couple hours teaching me about last design. During our conversation, Kevin pointed out a couple of ways to improve my current lasts. For example, to provide a secure but comfortable fit, last dimensions should be undersized in certain areas but not in foot sections which need to change dimensions under load.
In light of Kevin's suggestions, I've started planning a new CAD model which will combine the best points of my current lasts and the things I learned from visiting Leahy Custom Hiking Boots.