But I don't understand your last sentence about finding the skill contribution to potential cap via DMI, I believe this is not possible like that.
I think the best way to explain myself is by giving an example (I'm pulling data out of my head and not using a calculator; it's just an example):
Let's say you have a guard with all 6 guard skills trained to 15 (marvelous) and a potential of MVP. He has DMI of 2.500.000 . You know that MVP caps at around 2.700.000 - 3.000.000. And let's say you know this:
JR pop from 15-16: +50.000 DMI; from 16-17: 90.000 DMI
PA pop from 15-16: +40.000 DMI; from 16-17: 75.000 DMI
OD pop from 15-16: +30.000 DMI; from 16-17: 55.000 DMI
And so on. Now you can predict pretty accurately when will your player cap and you can choose which skills to train accordingly to that.
That's what I meant, I hope I made myself clear...