Heya,
I have a spreadsheet that calculates this stuff for you:
https://docs.google.com/spreadsheet/...Wc&usp=sharing
Please download and use offline (don't modify mine if you don't mind, I'll just have to roll back).
You can set your Skill Difficulty, your main stat, and your sill, and modify the trivial boxes to figure stuff out. I used it to level JC on Fippy.
Enjoy,
Tomtee