Quote: "When I read that, I imagine you saying that to me face (obviously preparing to run away). I can easily envisage you saying "Let's face it." then pausing for a long time for dramatic effect before delivering the threat. To me that suggests a comma isn't suitable.
"I take issue with you, your face, and your argument!" If you put large pauses where the commas would be, it just wouldn't work. "
Good, you're thinking on the right track. So that eliminates the comma from your list.

You can see one reason why I posted an argument 'for' using a colon in my first reply.
A colon could create a pause, not a very big one, but bigger than a comma. In speech you might have:
"I have a few items for you to collect [breathe in] I want a TV, a leather sofa, a packet of crisps, champagne and a Sex And The City DVD boxset." (Jokes on them, they can't watch that terrible show without a DVD player)
So now, lets try something else.
"Let's face it: you need a knuckle sandwich for not giving me the context."
It doesn't look right to me, not for speech anyway, maybe it works for other people, but personally I might do it differently. Here I might use an exclamation mark to emphasise the first clause. Yes, it would create 2 different sentences, but I'd argue it's permissable because you're breaking the 2 clauses to put emphasis on the first. An ellipsis "..." is useful for a different kind of emphasis, but it's not one I'd use in my last example.
An exclamation mark doesn't necessarily suggest a person is shouting, but it might suggest a slight change in their voice to draw attention to it. In an argument a person might say, "Let's face it!" to draw attention to the fact they're about to make a point and they won't need to emphasise what they're about to say because they've already got people's attention. In a situation where people are panicking, a person may do the same because they want everybody in the room to listen. If the person is Brian Blessed then it will all be in caps, it will use exclamation marks and you'll go deaf from reading it.
However, I think how you use your punctuation in dialogue mostly depends on how the character is meant to say it and context isn't the only factor here but characterisation too.
For example, here is the dialogue for one of my characters:
Quote: "
"I see they got you too." I say.
"Yeah. B...but." He stutters, "I'm not going to l...let them get to me. They..." he points a finger to his temple, "th...they get inside of your mind. They i...invade. They...they won't f...find what they want...ahaha! They're just going to have to just…kill me. I am u...unbreakable. Wh...what about you?"
He grips tight to the bars, his face is pressed; he points his right hand out and pulls it back in again. "You...you...why are you here?"
"
(can't remember if that's from my old draft or the revised one)
You might argue I've overused the ellipses, it needs to be represent the character's manic speech, yet at the same time be readable. The ellipses are to represent the breaking of speech, plus there's the repitition and short sentences. His mind is broken so he can only speak in chunks rather than a long consistent line of speech. So I am not worried about writing it if I were writing a covering letter for a job application nor am I worried about how the clauses are related to one and another just because of how this character speaks.
Also, because I write in first person perspective I try to employ the narrator's own voice.
One of the things about writing stylistically, particularly when it comes to dialogue is that you first understand grammar and how it works, find you have to break those rules where you see fit. The important thing about speech, which I think people sometimes forget, is that it's FULL of grammatical errors. Heck, a person's train of thought is grammatically incorrect too, so why should you force yourself to represent it in a grammatically correct fashion? Regardless, bear in mind text has to be readable. Hence my narrative, despite being the voice of my main character, complies more with standardised English than select characters who are either insane or speak in colloquialisms.
So when it comes to your dialogue, I think you're on the right track thinking about how you're using the pauses, because you're thinking how people speak. I think if you're trying to best represent speech, then just write it as it would be spoken. Then look at what you've written and see if it reads back as you imagined it and then ask how readable it is. Grammar helps with readability, hence we use standardised English.
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BatVink, I think that wins the argument right there.