In the game mechanics, the maximum benefit for minions is achieved at 60 knowledge points.
And what do combat machines have to do with it?
It might unlock, but try to get them in the game. What's the point of theoretical information that won't be used in practice?
Added 2 minutes ago
The maximum knowledge I've seen on a mage is 34. This was in a battle at 50 turns, played by a well-known YouTuber.
Added 6 minutes ago
I don't know who at the Heroes 5 developers calculated that with a CAP of 40 levels, mages would reach 60 knowledge.
ColouredText - список заклинаний и их уровень в описании существ-колдунов