Hm, to my mind from what I've seen and heard of the dialogue stances... part of the decision as to whether to go professional, suave, or aggressive would be based around you playing the spy adapting to whoever he's talking to..
So all the intel dossiers you pick up about other characters, what you might be learning about them before hand, will give hints of how they'll react to different stances you might use.. Thereby changing what options open up.
Case in point, it's been repeatedly mentioned that Sie is all about the aggressive, forceful, militant approach in conversations and will react more positively to you then if you're just purely trying to charm her in a James Bond suave style. So from the get go of any conversation you'll probably have an understanding of how to get a "good" response from any characters you've spent time picking up details on. Of course, you as the spy might be thinking "well, I can complete the mission without help from this person so I don't need to have them 'liking' me so I'll react anyway i want." Or you might still try the "let's not burn any bridges just yet and act in a way that they respect".
I guess what I'm groping in the dark for.. is that even with a timer during the actual conversation.. you'll have had time in game before hand to think about what stances work in what way with the different people you encounter.. At least, if you're paying any attention to the intel dossiers and rumours you pick up