Also purchased this game to only be disappointed by the lack of triple screen support. There are however some workarounds that may help resolve some of the issues.
Rear view mirror: Definitely doesn't scale properly. Go to
https://mafiamods.com and download a mod to remove the rear view mirror. Problem solved.
In Game Map: Go to In-Game options and and adjust the screen border under display settings. Your able to move it closer to the center monitor. Not the best but a start.
Main Menu: Definitely issues but workable after starting an initial game.
Other remaining issues:
-Zoomed in cut-scenes (not sure what to do here)
-Other zoomed in issues like the lockpick issue as others have mentioned.
It sounds like the developers are at least aware of the scaling issues at higher resolutions so hopefully we will get a workable patch soon. In the meantime, it may be best to play single monitor unfortunately
![Sad :(](./images/smilies/icon_e_sad.gif)