Boron: DL the App and test it yourself. I personally have found the app to be VERY useful, thanks Saber Cherry!
As for devils vs 200 militia: The critical mass is somewhere in mid 20's. While 23 Devils are the first group to win over 50% of their battles, 26 already wins over 90% and 28 wins 99,9%. After you go past 30, the avg Deaths per battle start to quickly decline and not even extreme odds help the militia anymore as even if you run huge amounts of battles, the win rate for devils is flat 100%.
The key concept of cource is that the devils are surrounded. Their primary line of defence is the strong Def and high hit points, having 9 militaman poking a devil with sharp sticks at the same time is of cource bad. Once you have enough devils that they form a coherent enough line (in real game situations storm actually helps here), they start to win easily even if you up the number of militia. For the same reason, 70 principes perform considerably worse against devils, losing 99.9% of the time against just 20 devils...
All in all devils still seem a bargain for their price
