play!Constanze realizes what Salieri is up to far earlier and also maintains the emotional upper hand with her contemptuous laughing at his pseudo-romantic dialogue and refusal to let him dress up this as anything but what it is/would be, his changing his mind about going through with it comes across as in response to this so he can save face, and she's furious.

Yesssss! I really loved this take on Constanze (and really loved this production's pragmatic and hard-edged Constanze). That's interesting that the dialogue is near identical! In the director's cut does she actually say "let's get this over with" (or whatever the line is)? And yes, they both work, although the vulnerability of movie!Constanze I think would set off my humiliation squick a bit, and I personally prefer the play version. (Well, I'm extrapolating since I haven't actually seen the director's cut, but.)