I had a minor breakthrough.
Designing custom nuts and saddles to determine optimum dimensions was becoming too complex because each change was addressing string spacing, fretboard edge gap, and neck width. To do this right, I need to isolate these parameters and study the effect of each individually.
So, instead of making new nuts and saddles, I'm simply using my 41mm nut and my 57mm saddle and sliding them to the left or right in order to study the relationship between the high E string and the fretboard edge.
Focusing on spacing at the nut and 12th fret, and adjusting each in 0.25mm increments, I have determined that the minimum spacing to eliminate string slippage off the edge of the fretboard to be 3.5mm at the nut and 4.5mm at the 12th fret, with string height of 2.0mm at the 12th fret. If the action is raised from 2.0mm, the distance would need to be increased.
I don't know if I'm using hard or extra hard tension strings, because I'm simply using whatever came with the guitar, but this combination of string height and fretboard edge gap allows me to play with reckless abandon, as fast as I can, without slippage. Reducing the gap to 4.25mm at the 12th fret, while maintaining 3.5mm at the nut, does result in occasional slipping. Since we are entertaining the possible dimensions of a production model guitar, it's important for someone of any playing style to have an enjoyable playing experience, and this distance is the absolute minimum to avoid slippage. Keep in mind that a classical guitar typically has an edge gap of 4.5mm at the nut and 6.0mm at the 12th fret. Again, higher string tension and lower string action are the magic ingredients that allow a classical guitar to be transformed into a crossover.
This produces a simple formula:
2(3.5mm) + desired string spacing at nut = neck width at nut
2(4.5mm) + desired string spacing at 12th fret = neck width at 12th fret
2(desired string spacing at 12th fret) - desired string spacing at nut = string spacing at saddle.
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