Restating the assumptions
OK, going back to the original goals, here's what I've understood from the discussion:
1) Ratio of farmers/commoners to non-farmers/commoners:
This ranges from 15:1 (for extremely primitive and hard agriculture) through 9:1 (typical medieval european) to 4:1 (Civil War era US), or stated in terms of percentages from 97% through 90% to 80%. Our general conclusion seems to be that magic use could shave another 5-20% from that, depending on the levels of magic. High levels of magic also seem to imply high numbers of elite PCs, so these should probably be directly related.
1b) The PC classes seem to range from 1-5% of the total population. 1% is roughly the 1e ratio, and represents a fairly fairly low (though full access) level of magic. Oathbound (an epic setting designed to handle extremely high power levels) quotes a 5%. The remainder would be the other NPC classes.
This does assume that the non-farming commoners and the farming commoners are a wash. OTOH, I'm not sure how big a difference it makes, since that lower boundary doesn't affect the PC/NPC boundary.
I'd also suggest the following mapping:
Magic Level__PC %__Base Ratio Improvement
Low________1_____5-8%
Medium_____2_____9-11%
High_______3_____12-14%
Ex. High____4_____15-17%
Absolute___5______18-20%
2) The corresponding ratio of each NPC class to each other.
3) The corresponding ratio of each PC class to each other.
Still not completely know, but seasong's "rarity" analysis should give the overall results.
4) The mortality/advancement curves for each class.
The overall agreement seems to be that some CR-based curve (with diminishing returns) is the answer, and that the peak numbers (median, mode, or mean) should be in the level 3-5 range. I'd suggest pegging it at 5, as this is an EL +4 counter for a LV1 party.
5) The settlement size divisions.
Still seems to be some question here: the standard pseudo-medieval city caps out somewhere between 50-100K. However, the large teeming fantasy metropolis (Ed Greenwood aside) seems to be a popular fantasy trope, and I just can't seem to reconcile 30K (the size of my home-cow-tipping-town) with "teeming metropolis".
6) The ratio of size & number of settlements (i.e for every N thorps, yo have 1 village, or such like)
Again, mostly done, though the ones we have don't seem to capture everything we need them to.
7) Distilling all that into handy-dandy charts.
We're getting a LOT closer.
Did I miss anything?