Hey, I've registered the forum to ask the same question.
I always play combat on slow, and it still seems fast in massive clashes. There are too many things happening to let the game flow for any reasonable time. As a result, I constantly have to press Pause, evaluate the situation/adjust orders, then unpause just to pause again less than in a second.
I'm not sure what is the right speed decrease for me, maybe 4x... If there is a way to try it out by adjusting something in gamefiles pls clarify.